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/tailwind.config.js

@@ -0,0 +1,27 @@
+/** @type {import('tailwindcss').Config} */
+export default {
+  content: ["./index.html", "./src/**/*.{ts,tsx}"],
+  theme: {
+    extend: {
+      colors: {
+        border: "hsl(var(--border))",
+        input: "hsl(var(--input))",
+        ring: "hsl(var(--ring))",
+        background: "hsl(var(--background))",
+        foreground: "hsl(var(--foreground))",
+        primary: { DEFAULT: "hsl(var(--primary))", foreground: "hsl(var(--primary-foreground))" },
+        secondary: { DEFAULT: "hsl(var(--secondary))", foreground: "hsl(var(--secondary-foreground))" },
+        muted: { DEFAULT: "hsl(var(--muted))", foreground: "hsl(var(--muted-foreground))" },
+        accent: { DEFAULT: "hsl(var(--accent))", foreground: "hsl(var(--accent-foreground))" },
+        destructive: { DEFAULT: "hsl(var(--destructive))", foreground: "hsl(var(--destructive-foreground))" },
+        card: { DEFAULT: "hsl(var(--card))", foreground: "hsl(var(--card-foreground))" },
+      },
+      borderRadius: {
+        lg: "var(--radius)",
+        md: "calc(var(--radius) - 2px)",
+        sm: "calc(var(--radius) - 4px)",
+      },
+    },
+  },
+  plugins: [],
+};