feat(udt-011): register TimeProvider.System in AddApplication DI

src/api/SIGCM2.Application/DependencyInjection.cs

@@ -67,6 +67,9 @@ public static class DependencyInjection
 {
     public static IServiceCollection AddApplication(this IServiceCollection services)
     {
+        // UDT-011: TimeProvider singleton — available to all handlers for Cat2 date computation
+        services.AddSingleton(TimeProvider.System);
+
         // Command handlers
         services.AddScoped<ICommandHandler<LoginCommand, LoginResponseDto>, LoginCommandHandler>();
         services.AddScoped<ICommandHandler<RefreshCommand, RefreshResponseDto>, RefreshCommandHandler>();