- Implement new /covers/proxy endpoint to cache and rewrite external LAN cover URLs
- Add url/urlencoding dependencies for URL parsing/escaping in pmocontrol and pmocovers Cargo.toml
- Transform album_art_uri fields to use proxy endpoint for LAN URLs in REST and SSE handlers (browse_container, MetadataChanged)
- Add URL validation logic to detect LAN vs public URLs and avoid self-caching
- Update Cargo.lock with new dependencies