fix: use iTunes names instead of kuromoji for Spotify Japanese tracks

Search iTunes with original Japanese names (accurate) rather than
pre-converting with kuromoji (inaccurate for uncommon names/readings).
iTunes returns the correct English artist name and title directly.
Also run iTunes enrichment for single-track Spotify imports.

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

backend/novasonic-server.js

@@ -225,13 +225,6 @@ app.post('/api/spotify/resolve', async (req, res) => {
       setTimeout(() => reject(new Error('Zeitüberschreitung — Spotify API antwortet nicht (>120s)')), 120000)
     );
     const data = await Promise.race([_resolveSpotifyViaSpotdl(url), timeout]);
-    // Normalize Japanese artist/title names to romaji before sending to frontend
-    if (data.tracks) {
-      for (const t of data.tracks) {
-        if (t.artistName) t.artistName = romajiForStorage(t.artistName) || t.artistName;
-        if (t.trackName)  t.trackName  = romajiForStorage(t.trackName)  || t.trackName;
-      }
-    }
     res.json(data);
   } catch(e) {
     console.error('[spotify/resolve]', e.message);