feat(dashboard): React frontend scaffold with overview page

- Vite + React 18 + TypeScript + Tailwind CSS
- Dashboard overview with health gauge, pillar bars, alerts
- WebSocket hook for real-time updates
- Layout with sidebar navigation and live indicator
- Placeholder pages for Mesh, Environment, Config, Alerts
- Dark theme ops center aesthetic with JetBrains Mono

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

dashboard-frontend/src/App.tsx

@@ -0,0 +1,23 @@
+import { Routes, Route } from 'react-router-dom'
+import Layout from './components/Layout'
+import Dashboard from './pages/Dashboard'
+import Mesh from './pages/Mesh'
+import Environment from './pages/Environment'
+import Config from './pages/Config'
+import Alerts from './pages/Alerts'
+
+function App() {
+  return (
+    <Layout>
+      <Routes>
+        <Route path="/" element={<Dashboard />} />
+        <Route path="/mesh" element={<Mesh />} />
+        <Route path="/environment" element={<Environment />} />
+        <Route path="/config" element={<Config />} />
+        <Route path="/alerts" element={<Alerts />} />
+      </Routes>
+    </Layout>
+  )
+}
+
+export default App