Add infrastructure layer with persistence and services

- EF Core DbContext and entity configurations
- Design-time factory for migrations
- Initial and soft-delete migrations
- Service implementations: Account, AccountYear, Entry,
  BalanceQuery, FileSave, PdfStatement
- Dependency injection registration

src/Duempelkas.Infrastructure/Services/AccountService.cs

@@ -0,0 +1,93 @@
+using Duempelkas.App.Services;
+using Duempelkas.App.Services.Models;
+using Duempelkas.Domain.Entities;
+using Duempelkas.Domain.Enums;
+using Duempelkas.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore;
+
+namespace Duempelkas.Infrastructure.Services;
+
+public class AccountService : IAccountService
+{
+    private readonly FinanceDbContext _db;
+
+    public AccountService(FinanceDbContext db) => _db = db;
+
+    public async Task<List<AccountSummaryDto>> GetAllAccountsAsync()
+    {
+        var accounts = await _db.Accounts
+            .Include(a => a.Entries)
+            .OrderBy(a => a.Name)
+            .ToListAsync();
+
+        return accounts.Select(MapToSummary).ToList();
+    }
+
+    public async Task<AccountSummaryDto> GetAccountAsync(int accountId)
+    {
+        var account = await _db.Accounts
+            .Include(a => a.Entries)
+            .FirstOrDefaultAsync(a => a.Id == accountId)
+            ?? throw new InvalidOperationException($"Account {accountId} not found.");
+
+        return MapToSummary(account);
+    }
+
+    public async Task<AccountSummaryDto> CreateAccountAsync(string name)
+    {
+        var account = new Account { Name = name };
+        _db.Accounts.Add(account);
+        await _db.SaveChangesAsync();
+        return new AccountSummaryDto(account.Id, account.Name, 0m, 0m, account.CreatedUtc);
+    }
+
+    public async Task RenameAccountAsync(int accountId, string newName)
+    {
+        var account = await _db.Accounts.FindAsync(accountId)
+            ?? throw new InvalidOperationException($"Account {accountId} not found.");
+        account.Name = newName;
+        await _db.SaveChangesAsync();
+    }
+
+    public async Task UpdateCarryoverAsync(int accountId, decimal carryoverBalance)
+    {
+        var account = await _db.Accounts.FindAsync(accountId)
+            ?? throw new InvalidOperationException($"Account {accountId} not found.");
+        account.CarryoverBalance = carryoverBalance;
+        await _db.SaveChangesAsync();
+    }
+
+    public async Task DeleteAccountAsync(int accountId)
+    {
+        var account = await _db.Accounts
+            .Include(a => a.Entries)
+            .FirstOrDefaultAsync(a => a.Id == accountId)
+            ?? throw new InvalidOperationException($"Account {accountId} not found.");
+
+        var entryIds = account.Entries.Select(e => e.Id).ToList();
+        var transferLinks = await _db.TransferLinks
+            .Where(tl => entryIds.Contains(tl.SourceEntryId) || entryIds.Contains(tl.TargetEntryId))
+            .ToListAsync();
+
+        foreach (var link in transferLinks)
+        {
+            var otherEntryId = entryIds.Contains(link.SourceEntryId) ? link.TargetEntryId : link.SourceEntryId;
+            var otherEntry = await _db.Entries.FindAsync(otherEntryId);
+            if (otherEntry != null)
+                _db.Entries.Remove(otherEntry);
+        }
+        _db.TransferLinks.RemoveRange(transferLinks);
+
+        _db.Accounts.Remove(account);
+        await _db.SaveChangesAsync();
+    }
+
+    private static AccountSummaryDto MapToSummary(Account account)
+    {
+        var totalIncome = account.Entries.Where(e => e.Type == EntryType.Income).Sum(e => e.Amount);
+        var totalExpense = account.Entries.Where(e => e.Type == EntryType.Expense).Sum(e => e.Amount);
+        var totalBalance = account.CarryoverBalance + totalIncome - totalExpense;
+
+        return new AccountSummaryDto(account.Id, account.Name, account.CarryoverBalance, totalBalance, account.CreatedUtc);
+    }
+}