fix: chain fs-routes guards with page loaders

[IzumiSy]

Summary

• chain file-based route guards with page loaders instead of letting the loader bypass guards
• keep existing fs-routes behavior when only guards or only a loader are defined
• add converter tests for module/resource guard+loader combinations

Testing

• pnpm --filter @tailor-platform/app-shell test -- src/fs-routes/converter.test.tsx