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/client.ts

@@ -49,7 +49,7 @@ class ApiError extends Error {
   }
 }
 
-async function request<T>(path: string, init?: RequestInit): Promise<T> {
+export async function request<T>(path: string, init?: RequestInit): Promise<T> {
   const res = await fetch(path, {
     headers: { "Content-Type": "application/json" },
     ...init,