feat: enterprise questpdf reports

- EmpresaReportService with 4 enterprise PDF reports
- ContratoAbierto: contract header, course detail, schedules, students
- ContratoCerrado: proposal info, courses, student list
- CotizacionCursoCerrado: quote header, course detail table
- CotizacionPlanCentral: company info, payment plan, course schedule
- EmpresaReportController with download endpoints
- All using ModuloEmpresa_PropuestaCrystalReport SP via Dapper

backend/src/Ventas.API/Program.cs

@@ -35,6 +35,8 @@ builder.Services.AddScoped<AlumnoService>(sp =>
 builder.Services.AddScoped<InformeService>(sp =>
     new InformeService(connectionString));
 builder.Services.AddScoped<ReportService>();
+builder.Services.AddScoped<EmpresaReportService>(sp =>
+    new EmpresaReportService(connectionString));
 
 var jwtSecret = builder.Configuration["Jwt:Secret"] ?? "default-dev-secret-change-in-production";
 var jwtExpiration = int.Parse(builder.Configuration["Jwt:ExpirationMinutes"] ?? "30");