Replace native add-folder dialogs with an in-app folder picker that supports collecting folders from multiple locations before adding them together.
Add backend directory listing and batch add commands with duplicate skipping, plus store actions and a themed picker UI with a dedicated folders-to-add panel.
Sets up Tauri v2 + React frontend with SQLite metadata store,
sqlite-vec for CLIP embedding infrastructure, and r2d2 connection
pool replacing the single Arc<Mutex<Connection>>. Indexer now uses
rayon for parallel file metadata collection.