fix: smooth NP swipe-open animation; live playing highlight in song lists

Swipe animation:
- _resetDrag(true) now reads the overlay's current drag position and starts
  the CSS transition from there instead of resetting to translateY(100%) first.
  That reset was causing the visible stutter (overlay jumped off-screen then
  slid back up). Now the overlay continues seamlessly from wherever the finger
  released to translateY(0).

Playing highlight:
- makeSongItem: adds data-song-id attribute to every .song-item element.
- updatePlayerUI: calls _updatePlayingHighlights() after every track change.
  This toggles .playing on all visible song items in any open list/playlist/
  favorites view so the highlighted row always matches what's actually playing,
  without requiring the user to navigate away and back.

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

src/player.js

@@ -356,6 +356,13 @@ export function playCurrent() {
     });
 }
 
+function _updatePlayingHighlights() {
+  const id = String(S.queue[S.qIdx]?.id ?? '');
+  document.querySelectorAll('.song-item[data-song-id]').forEach(el => {
+    el.classList.toggle('playing', el.dataset.songId === id);
+  });
+}
+
 export function updatePlayerUI(s, _skipMediaSession = false) {
   document.getElementById('player-title').textContent = s.title;
   const artistParts = (s.artist || '').split(/\s*(?:\/|•|,)\s*/).filter(Boolean);
@@ -387,6 +394,7 @@ export function updatePlayerUI(s, _skipMediaSession = false) {
     }));
   } catch {}
   _syncNpDirect(s);
+  _updatePlayingHighlights();
   // 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; }