Phase 1: Project scaffolding and infrastructure

- Scaffold Budget.Api (ASP.NET Core Web API, net10.0) with EF Core + Npgsql
- Scaffold Budget.Client (Vite + React + TypeScript) with /api proxy to localhost:5000
- Define all entity models: Budget, Income, Outgo, KnownUser, BudgetShare
- Configure AppDbContext with EF mappings and cascade deletes
- Add InitialCreate migration
- Configure SPA static file serving + fallback in Program.cs
- Add Dockerfile (multi-stage: node + dotnet sdk + aspnet runtime)
- Add .env.example with all required environment variables

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Budget.Api/Program.cs

@@ -0,0 +1,25 @@
+using Budget.Api.Data;
+using Microsoft.EntityFrameworkCore;
+
+var builder = WebApplication.CreateBuilder(args);
+
+var connStr = builder.Configuration.GetConnectionString("DefaultConnection")
+    ?? $"Host={builder.Configuration["POSTGRES_HOST"] ?? "localhost"};" +
+       $"Port={builder.Configuration["POSTGRES_PORT"] ?? "5432"};" +
+       $"Database={builder.Configuration["POSTGRES_DB"] ?? "budget"};" +
+       $"Username={builder.Configuration["POSTGRES_USER"] ?? "budget"};" +
+       $"Password={builder.Configuration["POSTGRES_PASSWORD"] ?? "changeme"}";
+
+builder.Services.AddDbContext<AppDbContext>(opt => opt.UseNpgsql(connStr));
+builder.Services.AddControllers();
+
+var app = builder.Build();
+
+app.UseDefaultFiles();
+app.UseStaticFiles();
+
+app.MapControllers();
+
+app.MapFallbackToFile("index.html");
+
+app.Run();