feat(frontend): add podman.live landing page + route split

Add a public marketing landing at "/" celebrating the Top-3 finish at the
AI Engineer World's Fair 2026 hackathon (2nd overall of 95+ teams, LiveKit
track + DigitalOcean Best Use), with a scroll-to-read hero, feature/tech
sections, and the demo embed.

Introduce react-router: "/" serves the public landing (no auth) and "/app"
mounts the existing Clerk-gated app. The app route degrades gracefully to a
"deploying" placeholder when no Clerk publishable key is configured, so the
site renders without secrets.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -30,6 +30,7 @@
     "react-day-picker": "^10.0.1",
     "react-dom": "^19.2.7",
     "react-resizable-panels": "^4.11.2",
+    "react-router-dom": "^7.18.1",
     "recharts": "3.8.0",
     "shadcn": "^4.12.0",
     "sonner": "^2.0.7",