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/addToQueue.ts

@@ -5,6 +5,7 @@
 
 import { deezerAPI } from '$lib/services/deezer';
 import { addToQueue } from '$lib/stores/downloadQueue';
+import { parseLyricsToLRC, parseLyricsToSYLT, parseLyricsText } from './tagger';
 
 /**
  * Fetch track metadata and add to download queue
@@ -19,7 +20,33 @@ export async function addDeezerTrackToQueue(trackId: string): Promise<void> {
     throw new Error('Track not found or invalid track ID');
   }
 
-  // Build track object
+  // Fetch album data for cover art URLs
+  let albumData = null;
+  try {
+    albumData = await deezerAPI.getAlbumData(trackInfo.ALB_ID.toString());
+  } catch (error) {
+    console.warn('[AddToQueue] Could not fetch album data:', error);
+  }
+
+  // Fetch lyrics
+  let lyricsData = null;
+  try {
+    lyricsData = await deezerAPI.getLyrics(trackInfo.SNG_ID.toString());
+  } catch (error) {
+    console.warn('[AddToQueue] Could not fetch lyrics:', error);
+  }
+
+  // Parse lyrics if available
+  let lyrics = undefined;
+  if (lyricsData) {
+    lyrics = {
+      sync: parseLyricsToLRC(lyricsData),
+      unsync: parseLyricsText(lyricsData),
+      syncID3: parseLyricsToSYLT(lyricsData)
+    };
+  }
+
+  // Build track object with enhanced metadata
   const track = {
     id: trackInfo.SNG_ID,
     title: trackInfo.SNG_TITLE,
@@ -36,10 +63,19 @@ export async function addDeezerTrackToQueue(trackId: string): Promise<void> {
     explicit: trackInfo.EXPLICIT_LYRICS === 1,
     md5Origin: trackInfo.MD5_ORIGIN,
     mediaVersion: trackInfo.MEDIA_VERSION,
-    trackToken: trackInfo.TRACK_TOKEN
+    trackToken: trackInfo.TRACK_TOKEN,
+    // Enhanced metadata
+    lyrics,
+    albumCoverUrl: albumData?.ALB_PICTURE ? `https://e-cdns-images.dzcdn.net/images/cover/${albumData.ALB_PICTURE}/500x500-000000-80-0-0.jpg` : undefined,
+    albumCoverXlUrl: albumData?.ALB_PICTURE ? `https://e-cdns-images.dzcdn.net/images/cover/${albumData.ALB_PICTURE}/1000x1000-000000-80-0-0.jpg` : undefined,
+    label: albumData?.LABEL_NAME,
+    barcode: albumData?.UPC,
+    releaseDate: trackInfo.PHYSICAL_RELEASE_DATE,
+    genre: trackInfo.GENRE ? [trackInfo.GENRE] : undefined,
+    copyright: trackInfo.COPYRIGHT
   };
 
-  // Add to queue
+  // Add to queue (queue manager runs continuously in background)
   await addToQueue({
     source: 'deezer',
     type: 'track',