feat(dl): add metadata, lyrics, and cover art tagging

Introduce metadata handling for online downloads:
- Embed cover art and lyrics (synced/unsynced) into MP3 files
- Save cover art to album folders and .lrc lyric files as sidecars
- Fetch and parse album/track metadata and lyrics from Deezer API
- Add user settings for artwork and lyrics embedding, LRC export, and cover quality
- Refactor queue manager to run continuously in background

src/lib/services/deezer/queueManager.ts

@@ -19,6 +19,7 @@ import type { DeezerTrack } from '$lib/types/deezer';
 export class DeezerQueueManager {
   private isProcessing = false;
   private abortController: AbortController | null = null;
+  private albumCoverCache: Map<string, Uint8Array> = new Map();
 
   /**
    * Start processing the queue
@@ -33,6 +34,9 @@ export class DeezerQueueManager {
     this.abortController = new AbortController();
     console.log('[DeezerQueueManager] Starting queue processor');
 
+    // Clear any stale currentJob from previous session
+    await setCurrentJob(null);
+
     try {
       await this.processQueue();
     } catch (error) {
@@ -57,16 +61,19 @@ export class DeezerQueueManager {
 
   /**
    * Main queue processing loop
+   * Runs continuously while the app is open, waiting for new items
    */
   private async processQueue(): Promise<void> {
+    console.log('[DeezerQueueManager] Queue processor started');
+
     while (this.isProcessing) {
       const queueState = get(downloadQueue);
       const nextItem = getNextQueuedItem(queueState);
 
       if (!nextItem) {
-        // No more items to process
-        console.log('[DeezerQueueManager] Queue empty, stopping');
-        break;
+        // No items to process - wait and check again
+        await new Promise(resolve => setTimeout(resolve, 500));
+        continue;
       }
 
       console.log(`[DeezerQueueManager] Processing item: ${nextItem.title}`);
@@ -99,6 +106,8 @@ export class DeezerQueueManager {
       // Clear current job
       await setCurrentJob(null);
     }
+
+    console.log('[DeezerQueueManager] Queue processor stopped');
   }
 
   /**