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/api/media.ts

@@ -0,0 +1,21 @@
+import { request } from "./client";
+import type { MediaMode, MediaState } from "../types/media";
+
+export function getMediaStatus(): Promise<MediaState> {
+  return request<MediaState>('/api/media/status');
+}
+
+export function queueMedia(source: string, mode: MediaMode): Promise<MediaState> {
+  return request<MediaState>('/api/media/queue', {
+    method: 'POST',
+    body: JSON.stringify({ source, mode }),
+  });
+}
+
+export function skipMedia(): Promise<MediaState> {
+  return request<MediaState>('/api/media/skip', { method: 'POST' });
+}
+
+export function stopMedia(): Promise<MediaState> {
+  return request<MediaState>('/api/media/stop', { method: 'POST' });
+}