feat(28-01): create useVuStore React hooks

- Add useAllVuLevels hook for subscribing to all VU levels
- Add useVuLevel hook for efficient single-mixer subscription
- Use useSyncExternalStore shim for React 16 compatibility
- Memoize getSnapshot callback to avoid unnecessary resubscription

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

jam-ui/src/hooks/useVuStore.js

@@ -0,0 +1,60 @@
+/**
+ * React hooks for subscribing to the external VU store
+ *
+ * Uses useSyncExternalStore shim for React 16 compatibility.
+ * Provides efficient subscription patterns for VU meter components.
+ */
+
+import { useSyncExternalStore } from 'use-sync-external-store/shim';
+import { useCallback } from 'react';
+import { vuStore } from '../stores/vuStore';
+
+/**
+ * Subscribe to all VU levels
+ *
+ * WARNING: Use sparingly - causes re-render on ANY VU change.
+ * Prefer useVuLevel for single mixer subscription.
+ *
+ * @returns {Object} - Map of mixerId to { level, clipping, timestamp }
+ *
+ * @example
+ * function AllVuMeters() {
+ *   const allLevels = useAllVuLevels();
+ *   return Object.keys(allLevels).map(mixerId => (
+ *     <VuMeter key={mixerId} mixerId={mixerId} level={allLevels[mixerId]} />
+ *   ));
+ * }
+ */
+export function useAllVuLevels() {
+  return useSyncExternalStore(
+    vuStore.subscribe,
+    vuStore.getSnapshot
+  );
+}
+
+/**
+ * Subscribe to single mixer's VU level
+ *
+ * More efficient than useAllVuLevels - only re-renders when this specific
+ * mixer's level changes.
+ *
+ * @param {string} mixerId - Qualified mixer ID (e.g., "M123" or "P456")
+ * @returns {Object|null} - { level, clipping, timestamp } or null if mixer not found
+ *
+ * @example
+ * function VuMeter({ mixerId }) {
+ *   const vuData = useVuLevel(mixerId);
+ *   if (!vuData) return null;
+ *   return <div>Level: {vuData.level}</div>;
+ * }
+ */
+export function useVuLevel(mixerId) {
+  // Create stable getSnapshot callback
+  // CRITICAL: Must be memoized with useCallback to avoid unnecessary resubscription
+  const getSnapshot = useCallback(() => vuStore.getLevelSnapshot(mixerId), [mixerId]);
+
+  return useSyncExternalStore(
+    vuStore.subscribe,
+    getSnapshot
+  );
+}