feat: migrate and redesign dashboard to modern React

- Full rewrite of legacy vanilla JS UI into React SPA
- Implement modern design system using Tailwind CSS and shadcn/ui primitives
- Create typed API modules and hooks for voice, media, and moderation
- Add new features: separated Music and Screen Share panels, Image Grid
- Implement unified WebSocket hook for real-time state and PCM audio
- Improve visualizer with smooth CSS transitions and live state sync
- Add __dirname polyfill for ES module compatibility
- Ensure responsive layout for mobile and desktop

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/hooks/useMediaControl.ts

@@ -0,0 +1,63 @@
+import { useCallback, useEffect, useState } from "react";
+import { getMediaStatus, queueMedia, skipMedia, stopMedia } from "../api/media";
+import type { MediaMode, MediaState } from "../types/media";
+
+const emptyMediaState: MediaState = { playing: false, current: null, queue: [] };
+
+export function useMediaControl() {
+  const [mediaState, setMediaState] = useState<MediaState>(emptyMediaState);
+  const [loading, setLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const refreshMedia = useCallback(async () => {
+    const state = await getMediaStatus();
+    setMediaState(state);
+    return state;
+  }, []);
+
+  const enqueue = useCallback(async (source: string, mode: MediaMode) => {
+    setLoading(true);
+    setError(null);
+    try {
+      const state = await queueMedia(source, mode);
+      setMediaState(state);
+      return state;
+    } catch (err) {
+      const message = err instanceof Error ? err.message : String(err);
+      setError(message);
+      throw err;
+    } finally {
+      setLoading(false);
+    }
+  }, []);
+
+  const skip = useCallback(async () => {
+    setLoading(true);
+    setError(null);
+    try {
+      const state = await skipMedia();
+      setMediaState(state);
+      return state;
+    } finally {
+      setLoading(false);
+    }
+  }, []);
+
+  const stop = useCallback(async () => {
+    setLoading(true);
+    setError(null);
+    try {
+      const state = await stopMedia();
+      setMediaState(state);
+      return state;
+    } finally {
+      setLoading(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    refreshMedia().catch((err) => setError(err instanceof Error ? err.message : String(err)));
+  }, [refreshMedia]);
+
+  return { mediaState, setMediaState, loading, error, refreshMedia, enqueue, skip, stop };
+}