fix(queue): optimistic shuffle toggle and aria-pressed for accessibility

toggleShuffle now sets this.shuffle before the backend call (like
cycleLoop does for loop mode), reverting on failure. Add aria-pressed
to the shuffle button so the E2E accessibility test detects state change.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pythoninthegrass

app/frontend/js/stores/queue.js

@@ -512,11 +512,14 @@ export function createQueueStore(Alpine) {
      */
     async toggleShuffle() {
       this._updating = true;
+      const prev = this.shuffle;
+      this.shuffle = !prev;
       try {
-        const snapshot = await queueApi.setShuffle(!this.shuffle);
+        const snapshot = await queueApi.setShuffle(this.shuffle);
         this._applySnapshot(snapshot);
       } catch (error) {
         console.error('[queue] toggleShuffle failed:', error);
+        this.shuffle = prev;
       } finally {
         setTimeout(() => {
           this._updating = false;

app/frontend/views/footer.html

@@ -151,6 +151,7 @@
       <button
         class="p-1 transition-colors"
         :class="isShuffleActive ? 'text-primary' : 'text-[#8E8E93] hover:text-foreground'"
+        :aria-pressed="isShuffleActive.toString()"
         @click="toggleShuffle()"
         title="Shuffle"
         data-testid="player-shuffle"