fix(backend): strip title-duplicate and generic words from album search suffix

Album "recognize - Single" produced query "MINA - recognize recognize Single"
because "recognize" appeared in both title and album name. Now filters album
words already present in the title, plus generic words (Single, EP, Remaster…).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/lib/ytdlp.js

@@ -128,8 +128,12 @@ async function downloadTrack({ jobId, artist, rawArtist, albumArtist, title, alb
   // This helps YTM rank the official OST/album track above fan covers and romaji-subtitle uploads.
   // Only use album words that are ASCII (romaji/English) — Japanese album words don't help YTM ranking.
   const hasJpTitle = JP_RE.test(title);
+  const GENERIC_ALBUM_WORDS = new Set(['single', 'ep', 'album', 'soundtrack', 'ost', 'edition', 'remaster', 'remastered', 'deluxe', 'bonus', 'version', 'live']);
+  const titleWordSet = new Set(title.toLowerCase().split(/\s+/));
   const albumWords = (album && album !== 'Singles' && album !== 'Unknown')
-    ? album.split(/\s+/).filter(w => /^[A-Za-z0-9]/.test(w)).slice(0, 2).join(' ')
+    ? album.split(/\s+/)
+        .filter(w => /^[A-Za-z0-9]/.test(w) && !titleWordSet.has(w.toLowerCase()) && !GENERIC_ALBUM_WORDS.has(w.toLowerCase()))
+        .slice(0, 2).join(' ')
     : '';
   const albumQuerySuffix = (hasJpTitle || (albumWords && titleKws.length <= 1)) && albumWords
     ? ' ' + albumWords : '';