fix: itunesProxy use 2-arg https.get matching existing working pattern, smarter fallback

- itunesProxy: drop 3-arg form (url, options, cb) — use 2-arg (url, cb) like lookupItunesTrackMeta
- _iGet: if proxy returns {results:[]} trust it (iTunes said no results); only fall back to direct Apple if proxy gave no response at all

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

backend/novasonic-server.js

@@ -488,7 +488,7 @@ function _spTrackItem(t, defaultAlbum, defaultArt, defaultAlbumArtist) {
 
 async function itunesProxy(url) {
   return new Promise((resolve, reject) => {
-    https.get(url, { headers: { 'User-Agent': 'iTunes/12.0' } }, res => {
+    https.get(url, res => {
       let d = '';
       res.on('data', c => d += c);
       res.on('end', () => { try { resolve(JSON.parse(d)); } catch { resolve({}); } });