fix: NP flicker, fully-random shuffle, playlist count backpatch

NP overlay flicker (stronger fix):
- Remove contain:layout style paint (causes layer issues on some Android WebView)
- Add ::before pseudo-element with solid background so no frame can be transparent
- Add -webkit-transform prefixes for both open and closed states

Shuffle fully random:
- playQueue no longer pins startIdx when shuffle is on
- All songs shuffled into a completely random order, S.qIdx=0 always
- toggleShuffle mid-queue still pins current song first (Spotify toggle behavior)

Playlist count wrong in overview:
- Navidrome's getPlaylists returns stale/wrong songCount in its index
- Add data-pl-id to each playlist card in loadPlaylists
- After loadPlaylistDetail gets the accurate entry count, backpatch the
  matching overview card's subtitle so the grid shows the real song count

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

styles.css

@@ -573,16 +573,20 @@ button:focus{outline:none}
   position:fixed;inset:0;z-index:300;
   display:flex;flex-direction:column;
   background:var(--bg);
-  /* translate3d keeps the element on a stable GPU layer without will-change's
-     layer-creation/destruction cycle that causes WebView to flash the content below */
   transform:translate3d(0,100%,0);
+  -webkit-transform:translate3d(0,100%,0);
   transition:transform .35s cubic-bezier(.4,0,.2,1);
   overflow:hidden;
   backface-visibility:hidden;-webkit-backface-visibility:hidden;
-  contain:layout style paint;
   isolation:isolate;
 }
-.np-overlay.open{transform:translate3d(0,0,0)}
+/* Solid opaque floor so no frame can ever be transparent to content below */
+.np-overlay::before{
+  content:'';position:absolute;inset:0;
+  background:var(--bg);z-index:-1;
+  transform:translateZ(0);
+}
+.np-overlay.open{transform:translate3d(0,0,0);-webkit-transform:translate3d(0,0,0)}
 
 /* Blurred album art as background — two layers for crossfade */
 .np-bg{