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/tenancy/routes/api/admin_modules.py

@@ -100,7 +100,7 @@ def _build_module_response(
     is_enabled: bool,
 ) -> ModuleResponse:
     """Build ModuleResponse from module code."""
-    from app.modules.enums import FrontendType  # API-007 - Enum for type safety
+    from app.modules.enums import FrontendType  # noqa: API-007 - Enum for type safety
 
     module = MODULES.get(code)
     if not module: