refactor(player): E.1 — extract queue-identity helpers to utils/ (#563)

Four pure helpers move out of playerStore: normalizeAnalysisTrackId,
sameQueueTrackId, queuesStructuralEqual, shallowCloneQueueTracks.
Adds focused unit tests for the stream:-prefix normalization and the
no-op detection that prevents unnecessary queue rewrites.

Behaviour preserved verbatim. playerStore 3618 → 3598 LOC.

src/store/playerStore.ts

@@ -24,6 +24,12 @@ import { resolveReplayGainDb } from '../utils/resolveReplayGainDb';
 import { shuffleArray } from '../utils/shuffleArray';
 import { songToTrack } from '../utils/songToTrack';
 import { buildInfiniteQueueCandidates } from '../utils/buildInfiniteQueueCandidates';
+import {
+  normalizeAnalysisTrackId,
+  queuesStructuralEqual,
+  sameQueueTrackId,
+  shallowCloneQueueTracks,
+} from '../utils/queueIdentity';
 import { getWindowKind } from '../app/windowKind';
 
 // Re-export for backward compatibility with the ~30 call sites that still
@@ -370,10 +376,6 @@ export function consumePendingQueueListScrollTop(): number | undefined {
   return v;
 }
 
-function shallowCloneQueueTracks(queue: Track[]): Track[] {
-  return queue.map(t => ({ ...t }));
-}
-
 function queueUndoSnapshotFromState(s: PlayerState): QueueUndoSnapshot {
   const scrollTop = readQueueListScrollTopForUndo();
   return {
@@ -476,28 +478,6 @@ function emitNormalizationDebug(step: string, details?: Record<string, unknown>)
   }).catch(() => {});
 }
 
-function normalizeAnalysisTrackId(trackId?: string | null): string | null {
-  if (!trackId) return null;
-  if (trackId.startsWith('stream:')) return trackId.slice('stream:'.length);
-  return trackId;
-}
-
-/** Compare track ids across `stream:` / bare Subsonic forms. */
-function sameQueueTrackId(a: string | undefined | null, b: string | undefined | null): boolean {
-  if (a == null || b == null) return false;
-  const na = normalizeAnalysisTrackId(a) ?? a;
-  const nb = normalizeAnalysisTrackId(b) ?? b;
-  return na === nb;
-}
-
-function queuesStructuralEqual(a: Track[], b: Track[]): boolean {
-  if (a.length !== b.length) return false;
-  for (let i = 0; i < a.length; i++) {
-    if (!sameQueueTrackId(a[i]?.id, b[i]?.id)) return false;
-  }
-  return true;
-}
-
 function normalizationAlmostEqual(a: number | null, b: number | null, eps = 0.12): boolean {
   if (a == null && b == null) return true;
   if (a == null || b == null) return false;