feat(medios,secciones): application layer + handlers TDD — ADM-001 B3+B4

- IMedioRepository, ISeccionRepository interfaces
- MediosQuery, SeccionesQuery common records
- TipoSeccion static AllowedTipos helper
- Medios: 6 use cases (Create/Update/Deactivate/Reactivate/List/GetById) with validators, handlers and DTOs
- Secciones: 6 use cases mirroring Medios; Create validates MedioId active via IMedioRepository
- 52 unit tests (xUnit + NSubstitute) all green; audit LogAsync asserted per mutating handler
- DI registrations for all 12 handlers and validators auto-scanned via AddValidatorsFromAssemblyContaining

tests/SIGCM2.Application.Tests/Medios/Update/UpdateMedioCommandHandlerTests.cs

@@ -0,0 +1,83 @@
+using NSubstitute;
+using SIGCM2.Application.Abstractions.Persistence;
+using SIGCM2.Application.Audit;
+using SIGCM2.Application.Medios.Update;
+using SIGCM2.Domain.Entities;
+using SIGCM2.Domain.Exceptions;
+
+namespace SIGCM2.Application.Tests.Medios.Update;
+
+public class UpdateMedioCommandHandlerTests
+{
+    private readonly IMedioRepository _repo = Substitute.For<IMedioRepository>();
+    private readonly IAuditLogger _audit = Substitute.For<IAuditLogger>();
+    private readonly UpdateMedioCommandHandler _handler;
+
+    private static Medio MakeMedio(int id = 1, string nombre = "Original", TipoMedio tipo = TipoMedio.Diario, bool activo = true)
+        => new(id, "COD" + id, nombre, tipo, null, activo, DateTime.UtcNow, null);
+
+    private static UpdateMedioCommand ValidCommand(int id = 1) => new(
+        Id: id,
+        Nombre: "Nuevo Nombre",
+        Tipo: TipoMedio.Radio,
+        PlataformaEmpresaId: 5);
+
+    public UpdateMedioCommandHandlerTests()
+    {
+        _handler = new UpdateMedioCommandHandler(_repo, _audit);
+    }
+
+    // ── not found → throws ──────────────────────────────────────────────────
+
+    [Fact]
+    public async Task Handle_NotFound_ThrowsMedioNotFoundException()
+    {
+        _repo.GetByIdAsync(999, Arg.Any<CancellationToken>()).Returns((Medio?)null);
+
+        await Assert.ThrowsAsync<MedioNotFoundException>(
+            () => _handler.Handle(new UpdateMedioCommand(999, "X", TipoMedio.Diario, null)));
+    }
+
+    // ── happy path ───────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task Handle_HappyPath_CallsUpdateAsyncOnce()
+    {
+        var medio = MakeMedio(1);
+        _repo.GetByIdAsync(1, Arg.Any<CancellationToken>()).Returns(medio);
+
+        await _handler.Handle(ValidCommand(1));
+
+        await _repo.Received(1).UpdateAsync(Arg.Any<Medio>(), Arg.Any<CancellationToken>());
+    }
+
+    [Fact]
+    public async Task Handle_HappyPath_ReturnsDtoWithUpdatedFields()
+    {
+        var medio = MakeMedio(1, "Original", TipoMedio.Diario);
+        _repo.GetByIdAsync(1, Arg.Any<CancellationToken>()).Returns(medio);
+
+        var result = await _handler.Handle(ValidCommand(1));
+
+        Assert.Equal(1, result.Id);
+        Assert.Equal("Nuevo Nombre", result.Nombre);
+        Assert.Equal(TipoMedio.Radio, result.Tipo);
+        Assert.Equal(5, result.PlataformaEmpresaId);
+    }
+
+    [Fact]
+    public async Task Handle_HappyPath_CallsAuditWithUpdateAction()
+    {
+        var medio = MakeMedio(1);
+        _repo.GetByIdAsync(1, Arg.Any<CancellationToken>()).Returns(medio);
+
+        await _handler.Handle(ValidCommand(1));
+
+        await _audit.Received(1).LogAsync(
+            action: "medio.update",
+            targetType: "Medio",
+            targetId: "1",
+            metadata: Arg.Any<object?>(),
+            ct: Arg.Any<CancellationToken>());
+    }
+}