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/DependencyInjection.cs

@@ -0,0 +1,24 @@
+using Duempelkas.App.Services;
+using Duempelkas.Infrastructure.Persistence;
+using Duempelkas.Infrastructure.Services;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Duempelkas.Infrastructure;
+
+public static class DependencyInjection
+{
+    public static IServiceCollection AddInfrastructure(this IServiceCollection services, string connectionString)
+    {
+        services.AddDbContext<FinanceDbContext>(options =>
+            options.UseSqlite(connectionString));
+
+        services.AddScoped<IAccountService, AccountService>();
+        services.AddScoped<IEntryService, EntryService>();
+        services.AddScoped<IBalanceQueryService, BalanceQueryService>();
+        services.AddScoped<IPdfStatementService, PdfStatementService>();
+        services.AddScoped<IFileSaveService, FileSaveService>();
+
+        return services;
+    }
+}