perf(player): debounce localStorage persistence

Wrap save() in a 300ms debounce to prevent rapid serialization
when multiple state changes fire in quick succession (e.g. removing
several items or adjusting volume).

src/lib/player/store.svelte.ts

@@ -26,6 +26,9 @@ class PlayerStore {
 	isMuted = $state(false);
 	uiOpen = $state(false); // Mobile UI state
 
+	// Debounce timer for save()
+	private _saveTimer: ReturnType<typeof setTimeout> | null = null;
+
 	// O(1) index: track.id → index in queue
 	private idToIndex = $derived.by(() => {
 		const map = new Map<number, number>();
@@ -99,6 +102,7 @@ class PlayerStore {
 	}
 
 	save() {
+		// Read snapshots synchronously so $effect tracks reactive deps
 		const data: PlayerState = {
 			queue: $state.snapshot(this.queue),
 			currentId: $state.snapshot(this.currentId),
@@ -109,7 +113,11 @@ class PlayerStore {
 			volume: $state.snapshot(this.volume),
 			isMuted: $state.snapshot(this.isMuted),
 		};
-		localStorage.setItem(STORAGE_KEY, JSON.stringify(data));
+		// Debounce only the serialization + write
+		if (this._saveTimer) clearTimeout(this._saveTimer);
+		this._saveTimer = setTimeout(() => {
+			localStorage.setItem(STORAGE_KEY, JSON.stringify(data));
+		}, 300);
 	}
 
 	// Actions