feat: complete fase 1 - all controllers, services, middleware

- Added Ejecutivo.cs entity
- ArqueoService + ArqueoController (arqueos por fecha/usuario)
- 13 missing controllers: Curso, Descuento, Documento, Empresa, Horario,
  Jornada, Programa, Propuesta, Region, Sala, Sede, Tarifa, Usuario
- JwtMiddleware.cs for cookie/token validation
- SpComplexQueries.cs for Dapper multi-resultset
- ArqueoService registered in DI
- Build: 0 errors
- Total: 21 controllers, 8 services, 7 repos, 21 entities

backend/src/Ventas.API/Program.cs

@@ -42,6 +42,8 @@ builder.Services.AddScoped<CotizacionService>(sp =>
     new CotizacionService(sp.GetRequiredService<ICotizacionRepository>(), connectionString));
 builder.Services.AddScoped<AlumnoService>(sp =>
     new AlumnoService(sp.GetRequiredService<IAlumnoRepository>(), connectionString));
+builder.Services.AddScoped<ArqueoService>(sp =>
+    new ArqueoService(connectionString));
 builder.Services.AddScoped<InformeService>();
 builder.Services.AddScoped<ReportService>();
 builder.Services.AddScoped<EmpresaReportService>(sp =>