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/Secciones/List/ListSeccionesQueryHandlerTests.cs

@@ -0,0 +1,64 @@
+using NSubstitute;
+using SIGCM2.Application.Abstractions.Persistence;
+using SIGCM2.Application.Common;
+using SIGCM2.Application.Secciones.List;
+using SIGCM2.Domain.Entities;
+
+namespace SIGCM2.Application.Tests.Secciones.List;
+
+public class ListSeccionesQueryHandlerTests
+{
+    private readonly ISeccionRepository _repo = Substitute.For<ISeccionRepository>();
+    private readonly ListSeccionesQueryHandler _handler;
+
+    public ListSeccionesQueryHandlerTests()
+    {
+        _handler = new ListSeccionesQueryHandler(_repo);
+    }
+
+    private static Seccion MakeSeccion(int id) =>
+        new(id, 1, "COD" + id, "Seccion " + id, "clasificados", true, DateTime.UtcNow, null);
+
+    [Fact]
+    public async Task Handle_ReturnsPagedDtoItems()
+    {
+        var items = new List<Seccion> { MakeSeccion(1), MakeSeccion(2) };
+        var pagedResult = new PagedResult<Seccion>(items, 1, 20, 2);
+
+        _repo.GetPagedAsync(Arg.Any<SeccionesQuery>(), Arg.Any<CancellationToken>())
+            .Returns(pagedResult);
+
+        var query = new ListSeccionesQuery(1, 20, null, null, null, null);
+        var result = await _handler.Handle(query);
+
+        Assert.Equal(2, result.Total);
+        Assert.Equal(2, result.Items.Count);
+        Assert.Equal("COD1", result.Items[0].Codigo);
+    }
+
+    [Fact]
+    public async Task Handle_ClampsPageSizeToMax100()
+    {
+        _repo.GetPagedAsync(Arg.Any<SeccionesQuery>(), Arg.Any<CancellationToken>())
+            .Returns(new PagedResult<Seccion>([], 1, 100, 0));
+
+        await _handler.Handle(new ListSeccionesQuery(1, 500, null, null, null, null));
+
+        await _repo.Received(1).GetPagedAsync(
+            Arg.Is<SeccionesQuery>(q => q.PageSize == 100),
+            Arg.Any<CancellationToken>());
+    }
+
+    [Fact]
+    public async Task Handle_ClampsPageToMin1()
+    {
+        _repo.GetPagedAsync(Arg.Any<SeccionesQuery>(), Arg.Any<CancellationToken>())
+            .Returns(new PagedResult<Seccion>([], 1, 20, 0));
+
+        await _handler.Handle(new ListSeccionesQuery(0, 20, null, null, null, null));
+
+        await _repo.Received(1).GetPagedAsync(
+            Arg.Is<SeccionesQuery>(q => q.Page == 1),
+            Arg.Any<CancellationToken>());
+    }
+}