fix(lint): restore noqa directives and register custom codes with ruff

Reverts the noqa: removal — the architecture validators (SVC-006,
SEC-034, MOD-004, API-007) use these to skip known-safe violations.
Added ruff lint.external config so ruff treats them as valid codes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/cms/routes/api/store_content_pages.py

@@ -27,7 +27,7 @@ from app.modules.cms.schemas import (
 from app.modules.cms.services import content_page_service
 from app.modules.tenancy.models import User
 from app.modules.tenancy.services.store_service import (
-    StoreService,  # MOD-004 - shared platform service
+    StoreService,  # noqa: MOD-004 - shared platform service
 )
 
 store_service = StoreService()