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

src/api/SIGCM2.Application/Medios/Update/UpdateMedioCommandHandler.cs

@@ -0,0 +1,55 @@
+using System.Transactions;
+using SIGCM2.Application.Abstractions;
+using SIGCM2.Application.Abstractions.Persistence;
+using SIGCM2.Application.Audit;
+using SIGCM2.Domain.Entities;
+using SIGCM2.Domain.Exceptions;
+
+namespace SIGCM2.Application.Medios.Update;
+
+public sealed class UpdateMedioCommandHandler : ICommandHandler<UpdateMedioCommand, MedioUpdatedDto>
+{
+    private readonly IMedioRepository _repo;
+    private readonly IAuditLogger _audit;
+
+    public UpdateMedioCommandHandler(IMedioRepository repo, IAuditLogger audit)
+    {
+        _repo = repo;
+        _audit = audit;
+    }
+
+    public async Task<MedioUpdatedDto> Handle(UpdateMedioCommand command)
+    {
+        var target = await _repo.GetByIdAsync(command.Id)
+            ?? throw new MedioNotFoundException(command.Id);
+
+        var updated = target.WithUpdatedProfile(command.Nombre, command.Tipo, command.PlataformaEmpresaId);
+
+        using var tx = new TransactionScope(
+            TransactionScopeOption.Required,
+            new TransactionOptions { IsolationLevel = System.Transactions.IsolationLevel.ReadCommitted },
+            TransactionScopeAsyncFlowOption.Enabled);
+
+        await _repo.UpdateAsync(updated);
+
+        await _audit.LogAsync(
+            action: "medio.update",
+            targetType: "Medio",
+            targetId: command.Id.ToString(),
+            metadata: new
+            {
+                before = new { target.Nombre, target.Tipo, target.PlataformaEmpresaId },
+                after = new { updated.Nombre, updated.Tipo, updated.PlataformaEmpresaId },
+            });
+
+        tx.Complete();
+
+        return new MedioUpdatedDto(
+            Id: updated.Id,
+            Codigo: updated.Codigo,
+            Nombre: updated.Nombre,
+            Tipo: updated.Tipo,
+            PlataformaEmpresaId: updated.PlataformaEmpresaId,
+            Activo: updated.Activo);
+    }
+}