feat: Implement offline library synchronization with IndexedDB

- Added `useOfflineLibrarySync` hook for managing offline library sync operations.
- Created `OfflineLibrarySync` component for UI integration.
- Developed `offlineLibraryDB` for IndexedDB interactions, including storing and retrieving albums, artists, songs, and playlists.
- Implemented sync operations for starred items, playlists, and scrobbling.
- Added auto-sync functionality when coming back online.
- Included metadata management for sync settings and statistics.
- Enhanced error handling and user feedback through toasts.

lib/navidrome.ts

@@ -330,6 +330,23 @@ class NavidromeAPI {
     return `${this.config.serverUrl}/rest/stream?${params.toString()}`;
   }
 
+  // Direct download URL (original file). Useful for offline caching where the browser can handle transcoding.
+  getDownloadUrl(songId: string): string {
+    const salt = this.generateSalt();
+    const token = this.generateToken(this.config.password, salt);
+
+    const params = new URLSearchParams({
+      u: this.config.username,
+      t: token,
+      s: salt,
+      v: this.version,
+      c: this.clientName,
+      id: songId
+    });
+
+    return `${this.config.serverUrl}/rest/download?${params.toString()}`;
+  }
+
   getCoverArtUrl(coverArtId: string, size?: number): string {
     const salt = this.generateSalt();
     const token = this.generateToken(this.config.password, salt);