fix(web): trigger audio.play() during 'loading' state, not only 'playing'

The layout's play-intent effect gated audioEl.play() on player.isPlaying
(state === 'playing'), but the state progression is loading → DOM play()
→ 'playing' event → state='playing'. Without calling play() during
loading, the DOM never starts, the event never fires, and state is
pinned to loading forever. Call play() for the intent-to-play union
(loading + playing), matching the store's design.

web/src/routes/+layout.svelte

@@ -53,7 +53,10 @@
 
   $effect(() => {
     if (!audioEl) return;
-    if (player.isPlaying) {
+    // "Intent to play" = loading or playing. During 'loading' the DOM hasn't
+    // emitted 'playing' yet, but we still need to call play() to get there.
+    const intent = player.state === 'playing' || player.state === 'loading';
+    if (intent) {
       audioEl.play().catch(() => { /* interrupted / blocked — store gets the event */ });
     } else {
       audioEl.pause();