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/pages/Environment.tsx

@@ -0,0 +1,15 @@
+import { Cloud } from 'lucide-react'
+
+export default function Environment() {
+  return (
+    <div className="flex flex-col items-center justify-center h-[60vh] text-center">
+      <div className="w-16 h-16 rounded-full bg-bg-card border border-border flex items-center justify-center mb-6">
+        <Cloud size={32} className="text-slate-500" />
+      </div>
+      <h2 className="text-xl font-semibold text-slate-300 mb-2">Environment</h2>
+      <p className="text-slate-500 max-w-md">
+        Environmental feeds and space weather detail coming soon
+      </p>
+    </div>
+  )
+}