docs: fix stale migration and endpoint counts, add missing endpoints

- Update migration count from 11 to 13 across all docs (012_bom_source,
  013_move_cost_sourcing_to_props)
- Update endpoint count from 75 to 78 across all docs
- Add 3 missing endpoints to SPECIFICATION.md section 11.1:
  GET /api/events (SSE), GET /api/items/by-uuid/{uuid},
  POST /api/items/{pn}/bom/merge
- Add migrations 012 and 013 to STATUS.md table
- Fix migration 010 description (sourcing_link and standard_cost moved
  to revision properties in 013)

docs/GAP_ANALYSIS.md

@@ -365,7 +365,7 @@ internal/
     handlers.go             # Items, schemas, projects, revisions
     middleware.go            # Auth middleware
     odoo_handlers.go        # Odoo integration endpoints
-    routes.go               # Route registration (75 endpoints)
+    routes.go               # Route registration (78 endpoints)
     search.go               # Fuzzy search
   auth/
     auth.go                 # Auth service: local, LDAP, OIDC