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/pages/store.py

@@ -14,7 +14,7 @@ from sqlalchemy.orm import Session
 from app.api.deps import get_current_store_from_cookie_or_header, get_db
 from app.modules.cms.services import content_page_service
 from app.modules.core.services.platform_settings_service import (
-    platform_settings_service,  # MOD-004 - shared platform service
+    platform_settings_service,  # noqa: MOD-004 - shared platform service
 )
 from app.modules.tenancy.models import Store, User
 from app.templates_config import templates