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/Common/MediosQuery.cs

@@ -0,0 +1,12 @@
+using SIGCM2.Domain.Entities;
+
+namespace SIGCM2.Application.Common;
+
+/// <summary>Query parameters for listing medios with optional filters and paging.</summary>
+public sealed record MediosQuery(
+    int Page,
+    int PageSize,
+    bool? Activo,
+    TipoMedio? Tipo,
+    string? Search
+);

src/api/SIGCM2.Application/Common/SeccionesQuery.cs

@@ -0,0 +1,11 @@
+namespace SIGCM2.Application.Common;
+
+/// <summary>Query parameters for listing secciones with optional filters and paging.</summary>
+public sealed record SeccionesQuery(
+    int Page,
+    int PageSize,
+    int? MedioId,
+    string? Tipo,
+    bool? Activo,
+    string? Search
+);