refactor+feat(backend): ChargeableCharConfig por ProductType + Reactivate + Delete endpoints (PRC-001)

Part A — MedioId → ProductTypeId rename across all C# layers:
  Domain, Application, Infrastructure, API, all test projects.
  Solution was non-compilable after BD refactor (5c1675e); now compiles clean (0 errors).

Part B — PATCH /api/v1/admin/chargeable-chars/{id}/reactivate:
  ReactivateChargeableCharConfigCommand/Handler, SP guard maps 50410/50411/50412
  → ChargeableCharConfigReactivationNotAllowedException(Reason) → HTTP 409.

Part C — DELETE /api/v1/admin/chargeable-chars/{id}:
  DeleteChargeableCharConfigCommand/Handler, physical DELETE on SYSTEM_VERSIONED table.
  KeyNotFoundException → 404 via ExceptionFilter.

Tests: +30 unit tests (TDD RED→GREEN). All 1266 unit tests pass.

tests/SIGCM2.Application.Tests/Pricing/ChargeableChars/CreateChargeableCharConfigHandlerTests.cs

@@ -37,7 +37,7 @@ public class CreateChargeableCharConfigHandlerTests
     }
 
     private static CreateChargeableCharConfigCommand ValidCmd(DateOnly? validFrom = null) => new(
-        MedioId: null,
+        ProductTypeId: null,
         Symbol: "$",
         Category: ChargeableCharCategories.Currency,
         PricePerUnit: 1.5m,
@@ -80,9 +80,9 @@ public class CreateChargeableCharConfigHandlerTests
     }
 
     [Fact]
-    public async Task Handle_WithMedioId_PassesMedioIdToRepo()
+    public async Task Handle_WithProductTypeId_PassesProductTypeIdToRepo()
     {
-        var cmd = ValidCmd() with { MedioId = 7 };
+        var cmd = ValidCmd() with { ProductTypeId = 7 };
 
         await _handler.Handle(cmd);