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/routes/+layout.svelte

@@ -6,6 +6,7 @@
   import { settings, loadSettings } from '$lib/stores/settings';
   import { scanPlaylists, type Playlist } from '$lib/library/scanner';
   import { downloadQueue } from '$lib/stores/downloadQueue';
+  import { deezerQueueManager } from '$lib/services/deezer/queueManager';
 
   let { children } = $props();
 
@@ -22,6 +23,9 @@
   onMount(async () => {
     await loadSettings();
     await loadPlaylists();
+
+    // Start background queue processor
+    deezerQueueManager.start();
   });
 
   async function loadPlaylists() {

src/routes/downloads/+page.svelte

@@ -1,7 +1,6 @@
 <script lang="ts">
   import { onMount, onDestroy } from 'svelte';
   import { downloadQueue, clearCompleted, removeFromQueue, type QueueItem } from '$lib/stores/downloadQueue';
-  import { deezerQueueManager } from '$lib/services/deezer/queueManager';
 
   let queueItems = $state<QueueItem[]>([]);
 
@@ -15,9 +14,6 @@
         .map(id => state.queue[id])
         .filter(item => item !== undefined);
     });
-
-    // Start queue processor
-    deezerQueueManager.start();
   });
 
   onDestroy(() => {

src/routes/settings/+page.svelte

@@ -7,6 +7,11 @@
     setDeezerConcurrency,
     setDeezerFormat,
     setDeezerOverwrite,
+    setEmbedCoverArt,
+    setSaveCoverToFolder,
+    setEmbedLyrics,
+    setSaveLrcFile,
+    setCoverImageQuality,
     loadSettings
   } from '$lib/stores/settings';
   import { clearLibrary as clearLibraryDb } from '$lib/library/database';
@@ -17,6 +22,11 @@
   let currentDeezerConcurrency = $state<number>(1);
   let currentDeezerFormat = $state<'FLAC' | 'MP3_320' | 'MP3_128'>('FLAC');
   let currentDeezerOverwrite = $state<boolean>(false);
+  let currentEmbedCoverArt = $state<boolean>(true);
+  let currentSaveCoverToFolder = $state<boolean>(true);
+  let currentEmbedLyrics = $state<boolean>(true);
+  let currentSaveLrcFile = $state<boolean>(true);
+  let currentCoverImageQuality = $state<number>(90);
   let activeTab = $state<'library' | 'deezer' | 'advanced'>('library');
 
   onMount(async () => {
@@ -26,6 +36,11 @@
     currentDeezerConcurrency = $settings.deezerConcurrency;
     currentDeezerFormat = $settings.deezerFormat;
     currentDeezerOverwrite = $settings.deezerOverwrite;
+    currentEmbedCoverArt = $settings.embedCoverArt;
+    currentSaveCoverToFolder = $settings.saveCoverToFolder;
+    currentEmbedLyrics = $settings.embedLyrics;
+    currentSaveLrcFile = $settings.saveLrcFile;
+    currentCoverImageQuality = $settings.coverImageQuality;
   });
 
   $effect(() => {
@@ -34,6 +49,11 @@
     currentDeezerConcurrency = $settings.deezerConcurrency;
     currentDeezerFormat = $settings.deezerFormat;
     currentDeezerOverwrite = $settings.deezerOverwrite;
+    currentEmbedCoverArt = $settings.embedCoverArt;
+    currentSaveCoverToFolder = $settings.saveCoverToFolder;
+    currentEmbedLyrics = $settings.embedLyrics;
+    currentSaveLrcFile = $settings.saveLrcFile;
+    currentCoverImageQuality = $settings.coverImageQuality;
   });
 
   async function selectMusicFolder() {
@@ -196,6 +216,66 @@
               <label for="deezer-overwrite">Overwrite existing files</label>
             </div>
           </div>
+
+          <fieldset>
+            <legend>Metadata & Artwork</legend>
+
+            <div class="field-row">
+              <input
+                id="embed-cover"
+                type="checkbox"
+                bind:checked={currentEmbedCoverArt}
+                onchange={() => setEmbedCoverArt(currentEmbedCoverArt)}
+              />
+              <label for="embed-cover">Embed cover art in files</label>
+            </div>
+
+            <div class="field-row">
+              <input
+                id="save-cover"
+                type="checkbox"
+                bind:checked={currentSaveCoverToFolder}
+                onchange={() => setSaveCoverToFolder(currentSaveCoverToFolder)}
+              />
+              <label for="save-cover">Save cover art to album folder</label>
+            </div>
+
+            <div class="field-row">
+              <input
+                id="embed-lyrics"
+                type="checkbox"
+                bind:checked={currentEmbedLyrics}
+                onchange={() => setEmbedLyrics(currentEmbedLyrics)}
+              />
+              <label for="embed-lyrics">Embed lyrics in files</label>
+            </div>
+
+            <div class="field-row">
+              <input
+                id="save-lrc"
+                type="checkbox"
+                bind:checked={currentSaveLrcFile}
+                onchange={() => setSaveLrcFile(currentSaveLrcFile)}
+              />
+              <label for="save-lrc">Save .lrc lyric files (for Rockbox/FLAC)</label>
+            </div>
+
+            <div class="field-row-stacked">
+              <label for="cover-quality">Cover Image Quality</label>
+              <div class="slider-container">
+                <input
+                  id="cover-quality"
+                  type="range"
+                  min="60"
+                  max="100"
+                  bind:value={currentCoverImageQuality}
+                  onchange={() => setCoverImageQuality(currentCoverImageQuality)}
+                />
+                <span class="slider-value">{currentCoverImageQuality}%</span>
+              </div>
+              <small class="help-text">JPEG quality for cover images (default: 90%)</small>
+            </div>
+          </fieldset>
         </section>
       {:else if activeTab === 'advanced'}
         <section class="tab-content">