feat(udt-011): T400.10 — inject TimeProvider into all Application handlers

All command handlers that call domain mutators now inject TimeProvider
via constructor and use _timeProvider.GetUtcNow().UtcDateTime as the
explicit 'now' argument. Replaces previous direct DateTime.UtcNow usage.

src/api/SIGCM2.Application/Usuarios/Update/UpdateUsuarioCommandHandler.cs

@@ -14,17 +14,20 @@ public sealed class UpdateUsuarioCommandHandler : ICommandHandler<UpdateUsuarioC
     private readonly IRolRepository _rolRepository;
     private readonly IRefreshTokenRepository _refreshTokenRepository;
     private readonly IAuditLogger _audit;
+    private readonly TimeProvider _timeProvider;
 
     public UpdateUsuarioCommandHandler(
         IUsuarioRepository repository,
         IRolRepository rolRepository,
         IRefreshTokenRepository refreshTokenRepository,
-        IAuditLogger audit)
+        IAuditLogger audit,
+        TimeProvider timeProvider)
     {
         _repository = repository;
         _rolRepository = rolRepository;
         _refreshTokenRepository = refreshTokenRepository;
         _audit = audit;
+        _timeProvider = timeProvider;
     }
 
     public async Task<UsuarioDetailDto> Handle(UpdateUsuarioCommand cmd)
@@ -52,7 +55,7 @@ public sealed class UpdateUsuarioCommandHandler : ICommandHandler<UpdateUsuarioC
         }
 
         var fields = new UpdateUsuarioFields(cmd.Nombre, cmd.Apellido, cmd.Email, cmd.Rol, cmd.Activo);
-        var now = DateTime.UtcNow;
+        var now = _timeProvider.GetUtcNow().UtcDateTime;
 
         using (var tx = new TransactionScope(
             TransactionScopeOption.Required,