Add GitHub Copilot prompt files

- Step-by-step prompts for solution skeleton, domain model,
  DbContext mappings, application services, UI shell/pages,
  PDF export, and tests/validation

.github/prompts/01-solution-skeleton.prompt.md

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+---
+description: "Create the Duempelkas .NET 10 solution skeleton with Photino.Blazor desktop host, Razor class library, domain, infrastructure, and test projects"
+agent: "agent"
+---
+
+# Step 1: Solution Skeleton
+
+Create the complete .NET 10 solution structure for the Duempelkas cashbook/personal-finance application.
+
+## Projects
+
+| Project | SDK | Output | NuGet Packages | Project References |
+|---------|-----|--------|----------------|--------------------|
+| `src/Duempelkas.Desktop` | Microsoft.NET.Sdk | Exe | Photino.Blazor | App, Infrastructure |
+| `src/Duempelkas.App` | Microsoft.NET.Sdk.Razor | Library | — | Domain |
+| `src/Duempelkas.Domain` | Microsoft.NET.Sdk | Library | — | — |
+| `src/Duempelkas.Infrastructure` | Microsoft.NET.Sdk | Library | Microsoft.EntityFrameworkCore.Sqlite, Microsoft.EntityFrameworkCore.Design, QuestPDF | Domain, App |
+| `tests/Duempelkas.Tests` | Microsoft.NET.Sdk | Library | xunit, xunit.runner.visualstudio, Microsoft.NET.Test.Sdk, FluentAssertions | Domain, Infrastructure, App |
+
+All projects target `net10.0`, enable nullable reference types, and use implicit usings.
+
+## Key Files to Create
+
+- `src/Duempelkas.Desktop/Program.cs` — Photino.Blazor startup: register DI services (DbContext, application services), register root Blazor component `<App>`, configure window title and size, handle unhandled exceptions.
+- `src/Duempelkas.Desktop/wwwroot/index.html` — HTML host page with Bootstrap 5 CDN, app CSS link, and `<app>` root element.
+- `src/Duempelkas.App/Components/App.razor` — Root Blazor component with Router.
+- `src/Duempelkas.App/Components/Routes.razor` — Router pointing to `Duempelkas.App.Pages` assembly.
+- `src/Duempelkas.App/Components/Layout/MainLayout.razor` — Shell layout with sidebar/nav and main content area.
+- `src/Duempelkas.App/_Imports.razor` — Global usings for Microsoft.AspNetCore.Components, Duempelkas namespaces.
+
+## Conventions
+
+- File-scoped namespaces everywhere.
+- Root namespace matches folder structure: `Duempelkas.Desktop`, `Duempelkas.App`, etc.
+- Place the `.sln` file at the repository root.

.github/prompts/02-domain-model.prompt.md

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+---
+description: "Implement the EF Core entity classes and enums for Account, AccountYear, Entry, TransferLink, and EntryType"
+agent: "agent"
+---
+
+# Step 2: Domain Model
+
+Implement the domain entities under `src/Duempelkas.Domain`.
+
+## Entities
+
+### Account (`Entities/Account.cs`)
+- `int Id` (PK)
+- `string Name` (required, max 200)
+- `DateTime CreatedUtc`
+- `ICollection<AccountYear> AccountYears` (navigation)
+
+### AccountYear (`Entities/AccountYear.cs`)
+- `int Id` (PK)
+- `int AccountId` (FK → Account)
+- `int Year` (e.g. 2026)
+- `decimal OpeningBalance` — explicit carryover from the previous year, user-entered
+- `DateTime CreatedUtc`
+- `Account Account` (navigation)
+- `ICollection<Entry> Entries` (navigation)
+
+Constraint: unique on `(AccountId, Year)`.
+
+### Entry (`Entities/Entry.cs`)
+- `int Id` (PK)
+- `int AccountYearId` (FK → AccountYear)
+- `EntryType Type` — Income or Expense
+- `DateTime Date`
+- `string Title` (required, max 500)
+- `decimal Amount` — always positive; sign determined by Type
+- `int? TransferLinkId` (FK → TransferLink, nullable)
+- `DateTime CreatedUtc`
+- `AccountYear AccountYear` (navigation)
+- `TransferLink? TransferLink` (navigation)
+
+### TransferLink (`Entities/TransferLink.cs`)
+- `int Id` (PK)
+- `int SourceEntryId` (FK → Entry, unique)
+- `int TargetEntryId` (FK → Entry, unique)
+- `string? Note`
+- `DateTime CreatedUtc`
+- `Entry SourceEntry` (navigation)
+- `Entry TargetEntry` (navigation)
+
+Invariants enforced at service level:
+- SourceEntry.Type must be Expense
+- TargetEntry.Type must be Income
+- Both share the same Amount and Date
+
+### EntryType (`Enums/EntryType.cs`)
+```csharp
+public enum EntryType { Income = 0, Expense = 1 }
+```
+
+## Conventions
+- Use `decimal` for all monetary amounts.
+- Store amounts as positive; behaviour (add/subtract) comes from `EntryType`.
+- File-scoped namespaces, nullable enabled.

.github/prompts/03-dbcontext-mappings.prompt.md

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+---
+description: "Implement FinanceDbContext with fluent entity configurations, indexes, relationships, and SQLite connection setup"
+agent: "agent"
+---
+
+# Step 3: DbContext & Mappings
+
+Create `src/Duempelkas.Infrastructure/Persistence/FinanceDbContext.cs`.
+
+## DbSets
+- `DbSet<Account> Accounts`
+- `DbSet<AccountYear> AccountYears`
+- `DbSet<Entry> Entries`
+- `DbSet<TransferLink> TransferLinks`
+
+## Connection
+- Accept SQLite connection string via constructor options.
+- Default path: `Data Source=duempelkas.db` in the app's base directory.
+
+## Entity Configurations (use `OnModelCreating` with `IEntityTypeConfiguration<T>` or inline)
+
+### Account
+- `Name` required, max length 200.
+- Cascade delete → AccountYears.
+
+### AccountYear
+- Unique index on `(AccountId, Year)`.
+- `OpeningBalance` column type `decimal(18,2)`.
+- Cascade delete → Entries.
+
+### Entry
+- Index on `(AccountYearId, Date)`.
+- `Amount` column type `decimal(18,2)`.
+- `Type` stored as int.
+- Optional FK to TransferLink (`TransferLinkId`), restrict delete.
+
+### TransferLink
+- Unique index on `SourceEntryId`.
+- Unique index on `TargetEntryId`.
+- Relationships to SourceEntry and TargetEntry with `DeleteBehavior.Restrict`.
+
+## Notes
+- Use separate `IEntityTypeConfiguration<T>` classes in `Persistence/Configurations/`.
+- Do not auto-generate migrations; the initial migration will be created manually later.

.github/prompts/04-application-services.prompt.md

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+---
+description: "Define and implement application service interfaces and implementations for accounts, years, entries, transfers, balance queries, and file operations"
+agent: "agent"
+---
+
+# Step 4: Application Services
+
+## Interfaces (in `src/Duempelkas.App/Services/`)
+
+### IAccountService
+- `Task<List<AccountSummaryDto>> GetAllAccountsAsync()` — returns each account with its current total balance across all years.
+- `Task<AccountSummaryDto> CreateAccountAsync(string name)`
+- `Task RenameAccountAsync(int accountId, string newName)`
+- `Task DeleteAccountAsync(int accountId)`
+
+### IAccountYearService
+- `Task<List<AccountYearDto>> GetYearsForAccountAsync(int accountId)`
+- `Task<AccountYearDto> CreateYearAsync(int accountId, int year, decimal openingBalance)`
+- `Task<decimal> SuggestCarryoverAsync(int accountId, int year)` — calculates prior year's closing balance as suggestion.
+- `Task UpdateOpeningBalanceAsync(int accountYearId, decimal openingBalance)`
+
+### IEntryService
+- `Task<List<EntryDto>> GetEntriesAsync(int accountYearId)`
+- `Task<EntryDto> CreateEntryAsync(int accountYearId, EntryType type, DateTime date, string title, decimal amount)`
+- `Task CreateTransferAsync(int sourceAccountYearId, int targetAccountYearId, DateTime date, string title, decimal amount)` — atomically creates two entries + TransferLink.
+- `Task DeleteEntryAsync(int entryId)` — if linked transfer, deletes both sides atomically.
+- `Task UpdateEntryAsync(int entryId, DateTime date, string title, decimal amount)`
+
+### IBalanceQueryService
+- `Task<decimal> GetAccountTotalBalanceAsync(int accountId)` — OpeningBalance + sum(Income) - sum(Expense) across all years.
+- `Task<YearlySummaryDto> GetYearlySummaryAsync(int accountYearId)` — returns opening balance, total income, total expense, yearly movement, closing balance.
+
+### IPdfStatementService
+- `Task<byte[]> GenerateYearlyStatementAsync(int accountYearId)`
+
+### IFileSaveService
+- `Task<string?> SaveFileAsync(byte[] content, string suggestedFileName)` — abstracts native file-save dialog.
+
+## DTOs (in `src/Duempelkas.App/Services/Models/`)
+- `AccountSummaryDto` { Id, Name, TotalBalance, CreatedUtc }
+- `AccountYearDto` { Id, AccountId, Year, OpeningBalance }
+- `EntryDto` { Id, AccountYearId, Type, Date, Title, Amount, IsTransfer, TransferLinkId, LinkedAccountName }
+- `YearlySummaryDto` { OpeningBalance, TotalIncome, TotalExpense, YearlyMovement, ClosingBalance }
+
+## Implementations (in `src/Duempelkas.Infrastructure/Services/`)
+- Implement each interface using `FinanceDbContext`.
+- All balance calculations use the single formula: `OpeningBalance + sum(Income) - sum(Expense)`.
+- Transfer creation must be wrapped in a transaction.
+- Entry deletion must check for TransferLink and delete both sides if linked.
+
+## DI Registration
+- Create `src/Duempelkas.Infrastructure/DependencyInjection.cs` with `AddInfrastructure(this IServiceCollection, string connectionString)` extension method that registers DbContext and all services.
+
+## Conventions
+- File-scoped namespaces.
+- Async/await throughout.
+- No business logic in entities; all in services.

.github/prompts/05-ui-shell-and-pages.prompt.md

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+---
+description: "Build the Blazor Hybrid UI shell, dashboard page, account detail page, entry table, dialogs, and responsive styling"
+agent: "agent"
+---
+
+# Step 5: UI Shell & Pages
+
+Build all Blazor components in `src/Duempelkas.App/`.
+
+## Page: Dashboard (`Pages/Dashboard.razor`)
+- Route: `/`
+- Displays all accounts as responsive Bootstrap cards using `AccountCardList` and `AccountCard` components.
+- Each card shows account name and formatted total balance (Euro).
+- A "Create Account" button opens `AddAccountDialog`.
+- Clicking a card navigates to `/accounts/{id}`.
+
+## Page: Account Detail (`Pages/Accounts/AccountDetail.razor`)
+- Route: `/accounts/{AccountId:int}`
+- **Header area**: Account name, total balance (including carryover), year selector dropdown, "Add Year" button, "Export PDF" button.
+- **Main area**: Chronological entry table (oldest to newest) for the selected year.
+- "Add Entry" and "Add Transfer" buttons in a toolbar above the table.
+- Show yearly summary at the bottom: Opening balance, Year movement, Closing balance.
+
+## Components (in `Components/Accounts/`)
+
+### AccountCardList.razor
+- Renders a responsive grid of `AccountCard` components.
+
+### AccountCard.razor / AccountCard.razor.css
+- Card displaying account name and total balance.
+- Click handler for navigation.
+
+### AccountHeader.razor
+- Displays account name, total balance, year selector, action buttons.
+
+### YearSelector.razor
+- Dropdown to select the active year, fires `EventCallback<int>` on change.
+
+### EntryTable.razor / EntryTable.razor.css
+- Table with columns: Date, Title, Type badge, Amount.
+- Rows sorted oldest → newest.
+- Transfer rows get a distinct visual indicator (e.g., link icon, blue highlight).
+
+### EntryRow.razor
+- Single table row. Badge color: green for Income, red for Expense, blue for Transfer-linked.
+
+### ExportButton.razor
+- Calls `IPdfStatementService` then `IFileSaveService` to save the PDF.
+
+## Dialogs (in `Components/Dialogs/`)
+
+### AddAccountDialog.razor
+- Modal with Name input. Calls `IAccountService.CreateAccountAsync`.
+
+### AddYearDialog.razor
+- Modal with Year number input and Opening Balance input. Pre-fills suggested carryover. Calls `IAccountYearService.CreateYearAsync`.
+
+### AddEntryDialog.razor
+- Modal with Type selector, Date, Title, Amount. Calls `IEntryService.CreateEntryAsync`.
+
+### AddTransferDialog.razor
+- Modal with source/target account+year selectors, Date, Title, Amount. Calls `IEntryService.CreateTransferAsync`.
+
+## Styling
+- Use Bootstrap 5 utilities for responsive layout.
+- Custom CSS in `wwwroot/css/app.css` for type badges, card hover states, and table row highlights.
+- Currency formatting: `amount.ToString("N2")` + " €" suffix.
+
+## Conventions
+- Container/presentation split: pages load data, child components are presentational.
+- Use `@inject` for services.
+- Dialogs use a simple `bool IsVisible` pattern with backdrop overlay.

.github/prompts/06-pdf-export.prompt.md

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+---
+description: "Implement QuestPDF-based yearly account statement PDF generation with balance summaries"
+agent: "agent"
+---
+
+# Step 6: PDF Export
+
+Implement `PdfStatementService` in `src/Duempelkas.Infrastructure/Services/`.
+
+## PDF Document Structure
+
+Generate one PDF per account/year with the following sections:
+
+### Header
+- Account name (bold, large)
+- Year (e.g., "Statement 2026")
+- Generation date
+
+### Opening Balance Section
+- "Carryover from previous year: X.XX €"
+
+### Ledger Table
+- Columns: Date, Title, Type, Amount
+- Rows sorted chronologically (oldest → newest)
+- Type column shows "Income", "Expense", or "Transfer" (for linked entries)
+- Transfer rows should include a note like "→ TargetAccountName" or "← SourceAccountName"
+- Amount formatted as "1.234,56 €" (German locale)
+
+### Summary Footer
+1. "Carryover from previous year: X.XX €"
+2. "Current year result: X.XX €" (sum of incomes minus sum of expenses)
+3. "Final balance: X.XX €" (carryover + current year result)
+
+## Implementation Details
+- Use `QuestPDF.Fluent` API with `Document.Create(...)`.
+- Set `QuestPDF.Settings.License = LicenseType.Community` in startup.
+- Reuse `IBalanceQueryService.GetYearlySummaryAsync` and `IEntryService.GetEntriesAsync` to get the data — do NOT recalculate balances independently.
+- Return `byte[]` from `GenerateYearlyStatementAsync`.
+- Use A4 page size, reasonable margins, and professional typography.
+
+## Conventions
+- Keep the PDF layout in a single service method or split into private helper methods.
+- Use `CultureInfo("de-DE")` for number/currency formatting.

.github/prompts/07-tests-and-validation.prompt.md

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+---
+description: "Create xUnit tests for transfer consistency, balance calculations, carryover logic, and PDF export totals"
+agent: "agent"
+---
+
+# Step 7: Tests & Validation
+
+Create tests in `tests/Duempelkas.Tests/`.
+
+## Test 1: Transfer Consistency (`TransferServiceTests.cs`)
+
+### Scenario: CreateTransfer_CreatesLinkedExpenseAndIncome
+Given:
+- Account A and Account B exist
+- Both have AccountYear for 2026 with OpeningBalance = 0
+
+When:
+- A transfer of 100.00 EUR is created from A/2026 to B/2026 with title "Test Transfer"
+
+Then:
+- Exactly 2 entries are created in the database
+- Entry on A is `EntryType.Expense`, amount = 100.00
+- Entry on B is `EntryType.Income`, amount = 100.00
+- Both entries share the same date and title
+- Exactly 1 `TransferLink` exists linking the two entries
+- Account A total balance = -100.00
+- Account B total balance = +100.00
+
+### Scenario: DeleteTransfer_RemovesBothSides
+Given:
+- A transfer exists between A and B
+
+When:
+- The source entry is deleted via `IEntryService.DeleteEntryAsync`
+
+Then:
+- Both entries are removed
+- The TransferLink is removed
+- Account A and B balances return to 0
+
+## Test 2: Yearly Statement Calculation (`YearlyStatementCalculationTests.cs`)
+
+### Scenario: YearlySummary_CalculatesCorrectTotals
+Given:
+- Account with Year 2026, OpeningBalance = 500.00
+- Entries: Income 800.00, Income 400.00, Expense 200.00, Expense 250.00
+
+Then:
+- TotalIncome = 1200.00
+- TotalExpense = 450.00
+- YearlyMovement = 750.00
+- ClosingBalance = 1250.00
+
+### Scenario: YearlySummary_IncludesTransfersCorrectly
+Given:
+- Account A, Year 2026, OpeningBalance = 500.00
+- Income entry: 1000.00
+- Transfer out to Account B: 300.00 (creates Expense entry on A)
+
+Then:
+- A's TotalIncome = 1000.00
+- A's TotalExpense = 300.00
+- A's YearlyMovement = 700.00
+- A's ClosingBalance = 1200.00
+
+## Test Setup
+- Use EF Core `InMemory` or SQLite in-memory (`Data Source=:memory:`) for test database.
+- Wire up real service implementations against the test database.
+- Use `FluentAssertions` for readable assertions.
+- Arrange/Act/Assert pattern throughout.
+
+## Manual Verification Checklist (as code comments)
+1. Launch on Windows — app window opens with dashboard
+2. Launch on Linux — app window opens (requires WebKit2GTK)
+3. Create account → appears on dashboard with 0 balance
+4. Add year 2026 with carryover 500 → year appears in selector
+5. Add income/expense entries → table populates, balance updates
+6. Create transfer between accounts → both sides appear with transfer badge
+7. Export PDF → file saves, totals match on-screen values
+8. Delete transfer → both sides removed, balances correct