refactor(queue): track resolver + selectors (thin-state phase 2) (#859)

* refactor(queue): add queue track resolver (thin-state phase 2a)

Standalone resolver: QueueItemRef → Track via index batch
(library_get_tracks_batch, ≤100/call) → network getSong fallback (P8), into a
bounded LRU cache. Holds raw tracks; session star/rating overrides (F4) merged
on read via applyQueueOverrides. Sync getCachedTrack + subscribeQueueResolver
for selectors; resolveVisibleRange prefetches a [-50, +200] window; carries
queue-only flags from refs; invalidate drops entries after a sync succeeds.

Not wired into the store/UI yet — phase 2b does that.

* refactor(queue): extract toQueueItemRefs helper

Pure helper deriving thin QueueItemRefs from a Track[] queue (per-item
serverId, queue-only flags), shared by the persist partialize and the
upcoming phase-2b resolver bridge. No behaviour change.

* refactor(queue): resolver bridge + queue selectors (thin-state phase 2b)

Seed the resolver cache from the canonical queue (queueResolverBridge, a
windowed [-50, +200] seed around the current index) and add the stable queue
selectors (useQueueTrackAt / useCurrentTrack / useQueueItems).

Additive: the store stays queue: Track[]-canonical; consumers migrate onto the
selectors in phase 3, and the selector impls move to the resolver once
queue: Track[] is dropped in phase 4. No mutation or persist change — the
persisted queueItems keeps its single restore role (no dual-role clash).

* docs(changelog): on-demand queue track loading groundwork (#859)

CHANGELOG.md

@@ -141,6 +141,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 
+### Queue — on-demand track loading for very large queues
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#859](https://github.com/Psychotoxical/psysonic/pull/859)**
+
+* Continued groundwork for multi-thousand-track queues: track details are resolved on demand through a shared cache rather than all being held at once. No change to how the queue looks or behaves.
+
+
+
 ## Fixed
 
 ### In-page browse — virtual scroll and cover-art priority