- Add stopProviderFallback manifest field with backward compat for skipBuiltInFallback
- Expose stop_provider_fallback in extension JSON API
- Unify service and search provider chips into 4-per-row grid layout
- Enable Ask Before Download for extensions with quality options
- Force useExtensionProviders always-on (built-in providers retired)
- Update localization: Built-in -> Legacy, remove obsolete description text
- Clear hardcoded donor names list