refactor(player): E.7 — extract two small file-private helpers (#570)

`emitNormalizationDebug` (debug-mode trace forwarder, 15+ internal call
sites) and `isInOrbitSession` (Orbit-active guard used by next() and the
async fallback paths to suppress local queue extensions, 5 call sites)
move into dedicated modules under src/store/. Both were file-private —
no caller-side changes outside playerStore's own imports.

playerStore 3434 → 3415 LOC.

src/store/normalizationDebug.ts

@@ -0,0 +1,19 @@
+import { invoke } from '@tauri-apps/api/core';
+import { useAuthStore } from './authStore';
+
+/**
+ * Forward a structured normalization-pipeline trace to the Rust-side debug
+ * log file when Settings → Logging is set to **Debug**. A no-op otherwise,
+ * so the dozens of call sites in `playerStore` (refresh / backfill / engine
+ * sync / track-switch instrumentation) carry zero cost in normal mode.
+ *
+ * Errors invoking the Rust command are swallowed — this is best-effort
+ * instrumentation, not a playback dependency.
+ */
+export function emitNormalizationDebug(step: string, details?: Record<string, unknown>): void {
+  if (useAuthStore.getState().loggingMode !== 'debug') return;
+  void invoke('frontend_debug_log', {
+    scope: 'normalization',
+    message: JSON.stringify({ step, details }),
+  }).catch(() => {});
+}