fix: improve extension runtime safety, HTTP response URL, SongLink parsing, and recommended service for extensions

- Add 'url' field (final URL after redirects) to all extension HTTP responses and fix fetch polyfill to return final URL instead of original request URL
- Fix RunWithTimeout race condition: increase force-timeout from 1s to 60s to prevent concurrent VM access crashes, add nil guards
- Use lockReadyVM() for thread-safe VM access in GetPlaylistWithExtensionJSON and InvokeAction
- Handle mixed JSON types (string, null, array) in SongLink resolve API SongUrls field
- Fix recommended download service not showing for extension-based searches in download picker

.gitignore

@@ -77,6 +77,7 @@ flutter_*.log
 # Development tools
 tool/
 .claude/settings.local.json
+.playwright-mcp/
 
 # FVM Version Cache
 .fvm/