fix: address UI and performance issues in LocalLibrary

- Fix asset protocol scope for thumbnails in tauri.conf.json
- Homologate artist view controls to match album controls pattern
- Make artist grouping optional with dropdown (Off, A-Z)
- Change grid/list to single toggle button for artists
- Allow 3 lines for artist names in grid view
- Fix album card width to prevent title overflow
- Add throttling to artist image fetch to avoid rate limiting

src-tauri/tauri.conf.json

@@ -30,8 +30,11 @@
         "scope": [
           "$CACHE/qbz/**",
           "$CONFIG/qbz/**",
+          "$DATA/qbz/**",
+          "$LOCALDATA/qbz/**",
           "$HOME/.cache/qbz/**",
           "$HOME/.config/qbz/**",
+          "$HOME/.local/share/qbz/**",
           "$HOME/**",
           "/mnt/**",
           "/media/**",