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/06-pdf-export.prompt.md

@@ -0,0 +1,43 @@
+---
+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.