fix: preload hi-res NP cover on track change so overlay opens instantly

_crossfadeNpBg only preloaded the 1024px cover when the NP overlay was
already open. Opening it fresh showed the old cover for ~0.5s while the
new image downloaded. Preloading in updatePlayerUI caches it immediately.

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

src/player.js

@@ -381,6 +381,9 @@ export function updatePlayerUI(s, _skipMediaSession = false) {
     }));
   } catch {}
   _syncNpDirect(s);
+  // Preload the hi-res NP cover now so opening the overlay is instant
+  const _npCv = coverUrl(s.coverArt, 1024);
+  if (_npCv && _npCv !== _npBgLastUrl) { const _pre = new Image(); _pre.src = _npCv; }
 }
 
 let _npBgCurr = 'a';