feat(crm): Expediente — referencia única de trazabilidad del trámite (Fase D)

- Tabla crm.cases (expediente) con folio EXP2026-08-001 (next_folio entidad EXP,
  sin dirección). Nace al crear la Oportunidad y se hereda vía case_id a
  solicitud → cotización → operación → factura. advance_stage solo avanza.
- case_id (FK a crm.cases) en crm.opportunities/service_requests/quotes,
  ops.shipments y fin.invoices; propagación en sus create_*. Migración
  d4e5f6a7b8c9 reversible.
- Endpoints GET /v1/crm/cases, /cases/{id}, /cases/by-ref/{ref} con timeline
  (historia completa para UI y otros sistemas).
- Frontend: casesAPI, ruta /dashboard/crm/expedientes (lista + timeline vertical),
  chip "📁 Expediente" en solicitud/cotización, "Expedientes" en el sidebar.
- Consecutivo de folios sin tope (soporta >10,000,000/mes).
- 4 pruebas de expediente (minteo, propagación, timeline, no-retroceso). Suite en verde (113).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/api/v1/modules/crm/router.py

@@ -13,6 +13,7 @@ from . import permissions  # noqa: F401  (side-effect: registra permisos del CRM
 from .accounts.routes import router as accounts_router
 from .activities.routes import router as activities_router
 from .addresses.routes import router as addresses_router
+from .cases.routes import router as cases_router
 from .catalogs.routes import router as catalogs_router
 from .contacts.routes import router as contacts_router
 from .documents.routes import router as documents_router
@@ -43,6 +44,7 @@ router.include_router(leads_router)
 router.include_router(pipelines_router)
 router.include_router(opportunities_router)
 router.include_router(activities_router)
+router.include_router(cases_router)
 router.include_router(metrics_router)
 router.include_router(catalogs_router)
 router.include_router(uploads_router)