fix: cmdPrev retry-skip + show SongCard actions on touch devices

Two corner-case fixes for the prev-history + play-next feature:

1. cmdPrev only tried queue.prev() once. instance.playNext's auto-
   advance retry-skip pushes failed songs into the same history stack,
   so a single prev frequently lands on an unplayable song — returning
   "Cannot play previous song" while leaving queue.currentIndex stuck
   mid-failure (causing next() to skip past the actually-playing song).
   Retry up to 4 times so prev finds a playable history entry, matching
   the retry budget already used by playNext for auto-advance.

2. SongCard.song-actions has opacity:0 by default and is revealed via
   parent :hover. Touch devices have no hover, so all three action
   buttons (Play / Play Next / Add) were invisible to phone/tablet
   users. Add @media (pointer: coarse) → opacity:1 to always show on
   touch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/bot/instance.ts

@@ -498,13 +498,17 @@ export class BotInstance extends EventEmitter {
   }
 
   private async cmdPrev(): Promise<string> {
-    const prev = this.queue.prev();
-    if (prev) {
+    // Retry-skip up to 4 attempts: history can include failed songs
+    // that playNext's auto-advance retry-skipped past, so a single
+    // prev would otherwise land on an unplayable song and leave the
+    // queue's currentIndex stuck mid-failure.
+    for (let i = 0; i < 4; i++) {
+      const prev = this.queue.prev();
+      if (!prev) return "No previous song";
       const ok = await this.resolveAndPlay(prev);
-      if (!ok) return "Cannot play previous song";
-      return `Now playing: ${prev.name} - ${prev.artist}`;
+      if (ok) return `Now playing: ${prev.name} - ${prev.artist}`;
     }
-    return "No previous song";
+    return "Cannot play any previous songs (all failed to resolve)";
   }
 
   private cmdVol(cmd: ParsedCommand): string {