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/downloader.ts

@@ -6,6 +6,10 @@ import { fetch } from '@tauri-apps/plugin-http';
 import { writeFile, mkdir, remove, rename, exists } from '@tauri-apps/plugin-fs';
 import { generateBlowfishKey, decryptChunk } from './crypto';
 import { generateTrackPath } from './paths';
+import { tagMP3 } from './tagger';
+import { downloadCover, saveCoverToAlbumFolder } from './imageDownload';
+import { settings } from '$lib/stores/settings';
+import { get } from 'svelte/store';
 import type { DeezerTrack } from '$lib/types/deezer';
 
 export interface DownloadProgress {
@@ -88,9 +92,36 @@ export async function downloadTrack(
       decryptedData = encryptedData;
     }
 
-    // Write to temp file
-    console.log('Writing to temp file...');
-    await writeFile(paths.tempPath, decryptedData);
+    // Get user settings
+    const appSettings = get(settings);
+
+    // Download cover art if enabled
+    let coverData: Uint8Array | undefined;
+    if ((appSettings.embedCoverArt || appSettings.saveCoverToFolder) && track.albumCoverUrl) {
+      try {
+        console.log('Downloading cover art...');
+        coverData = await downloadCover(track.albumCoverUrl);
+      } catch (error) {
+        console.warn('Failed to download cover art:', error);
+      }
+    }
+
+    // Apply tags (currently MP3 only)
+    let finalData = decryptedData;
+    if (format === 'MP3_320' || format === 'MP3_128') {
+      console.log('Tagging MP3 file...');
+      finalData = await tagMP3(
+        decryptedData,
+        track,
+        appSettings.embedCoverArt ? coverData : undefined,
+        appSettings.embedLyrics
+      );
+    }
+    // TODO: Add FLAC tagging when library is ready
+
+    // Write tagged file to temp
+    console.log('Writing tagged file to temp...');
+    await writeFile(paths.tempPath, finalData);
 
     // Move to final location
     const finalPath = `${paths.filepath}/${paths.filename}`;
@@ -104,6 +135,27 @@ export async function downloadTrack(
 
     await rename(paths.tempPath, finalPath);
 
+    // Save LRC sidecar file if enabled
+    if (appSettings.saveLrcFile && track.lyrics?.sync) {
+      try {
+        const lrcPath = finalPath.replace(/\.[^.]+$/, '.lrc');
+        console.log('Saving LRC file to:', lrcPath);
+        await writeFile(lrcPath, new TextEncoder().encode(track.lyrics.sync));
+      } catch (error) {
+        console.warn('Failed to save LRC file:', error);
+      }
+    }
+
+    // Save cover art to album folder if enabled
+    if (appSettings.saveCoverToFolder && coverData) {
+      try {
+        console.log('Saving cover art to album folder...');
+        await saveCoverToAlbumFolder(coverData, paths.filepath, 'cover');
+      } catch (error) {
+        console.warn('Failed to save cover art to folder:', error);
+      }
+    }
+
     console.log('Download complete!');
     return finalPath;