refactor(queue): persist thin QueueItemRef list (thin-state phase 1) (#858)

* refactor(queue): persist thin QueueItemRef list (thin-state phase 1)

Introduce QueueItemRef ({ serverId, trackId, autoAdded?, radioAdded?,
playNextAdded? }) and persist the whole queue as a thin queueItems list,
superseding the queueRefs id list. Dual-write: the windowed queue: Track[]
stays as the index-off fallback; the in-memory store is unchanged.

hydrateQueueFromIndex now prefers queueItems (per-item serverId) and carries
the queue-only flags onto the hydrated tracks (the index doesn't store them),
with a queueRefs fallback for stores persisted before this change.

Phase 1 of the queue thin-state plan; no store/consumer changes yet.

* test(queue): cover legacy queueRefs-only upgrade in hydrate

* docs(changelog): queue section dividers kept on index restore (#858)

src/store/playerStore.persistence.test.ts

@@ -285,4 +285,25 @@ describe('partialize: localStorage queue window', () => {
     expect((partial.queue as unknown[]).length).toBe(0);
     expect(partial.queueIndex).toBe(0);
   });
+
+  it('persists the whole queue as thin queueItems (refs + serverId + flags), not just the window', () => {
+    const tracks = makeTracks(600);
+    tracks[3].radioAdded = true;
+    tracks[4].autoAdded = true;
+    usePlayerStore.setState({ queue: tracks, queueIndex: 300, queueServerId: 's1' });
+
+    const partial = getPartialize()(usePlayerStore.getState());
+    const items = partial.queueItems as {
+      serverId: string; trackId: string; radioAdded?: boolean; autoAdded?: boolean;
+    }[];
+
+    // windowed `queue` is capped, but queueItems carries the WHOLE queue
+    expect((partial.queue as unknown[]).length).toBe(501);
+    expect(items.length).toBe(600);
+    expect(partial.queueItemsIndex).toBe(300);
+    expect(items[0].serverId).toBe('s1');
+    expect(items[3].radioAdded).toBe(true);
+    expect(items[4].autoAdded).toBe(true);
+    expect(items[0].radioAdded).toBeUndefined();
+  });
 });