- Add idb-keyval dependency for IndexedDB support
- Configure persist middleware to use IndexedDB
- Improves persistence reliability in browser environments
## Subtitle Priority (Backend)
- Add download_subtitles() method to base downloader
- Implement Bilibili subtitle fetching with cookies support
- Implement YouTube subtitle fetching
- Support SRT and JSON3 format parsing
- Prioritize platform subtitles over Whisper transcription
## Mindmap Export Enhancements (Frontend)
- Add SVG vector export with proper viewBox handling
- Add XMind format export with Chinese character encoding fix
- Fix PNG/SVG export to capture full content by calling fit() before export
- Add JSZip dependency for XMind export
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>