fix(backend): back-fill the release year from iTunes on single-track downloads

embedMetadata already writes date/track/totaltracks/disc, but the single-track path's
"album already known" branch back-filled genre/total/disc/duration/track# from iTunes
and omitted the year — so a source track without a year got no `date` tag written.
Add !meta.year to the fetch trigger and merge genreMeta.year, so the release year is
set at download time like the other fields.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/novasonic-server.js

@@ -587,12 +587,13 @@ app.post('/api/download', async (req, res) => {
           log(jobId, `📋 Album: "${meta.album}"`);
           // Always fetch iTunes when any field is missing — durationMs is required for the yt-dlp
           // duration filter; without it any unrelated video that matches the title text gets downloaded.
-          if (!meta.genre || !meta.totalTracks || !meta.durationMs || !meta.trackNum) {
+          if (!meta.genre || !meta.totalTracks || !meta.durationMs || !meta.trackNum || !meta.year) {
             // Strip release-type suffixes before iTunes lookup so "recognize - Single" → "recognize"
             const RELEASE_SUFFIX_RE = /\s*[-–]\s*(?:(?:official\s+)?(?:music\s+)?(?:single|ep|lp|album|ost|soundtrack|remaster(?:ed)?|deluxe(?:\s+edition)?|bonus\s+tracks?|b-?sides?|version|edit)\b.*|(?:20|19)\d{2})\s*$/i;
             const itunesTitle = title.replace(RELEASE_SUFFIX_RE, '').trim() || title;
             const genreMeta = await lookupItunesTrackMeta(searchArtist, itunesTitle).catch(() => ({}));
             if (!meta.genre       && genreMeta.genre)       { meta.genre       = genreMeta.genre;       log(jobId, `📋 Genre: "${genreMeta.genre}"`); }
+            if (!meta.year        && genreMeta.year)        { meta.year        = genreMeta.year;        log(jobId, `📋 Jahr: ${genreMeta.year}`); }
             if (!meta.totalTracks && genreMeta.totalTracks) { meta.totalTracks = genreMeta.totalTracks; }
             if (!meta.discNum     && genreMeta.discNum)     { meta.discNum     = genreMeta.discNum;     }
             if (!meta.discTotal   && genreMeta.discTotal)   { meta.discTotal   = genreMeta.discTotal;   }