chore: optimize Vercel costs by removing analytics and configuring functions (#238)

- Create vercel.json with optimized function settings:
  - Chat API: 512MB memory, 120s timeout
  - Other APIs: 256MB memory, 10s timeout
- Remove @vercel/analytics package and imports
- Reduce chat route maxDuration from 300s to 120s

Expected savings: $2-4/month, keeping costs under $20 included credit

package.json

@@ -37,7 +37,6 @@
         "@radix-ui/react-switch": "^1.2.6",
         "@radix-ui/react-tooltip": "^1.1.8",
         "@radix-ui/react-use-controllable-state": "^1.2.2",
-        "@vercel/analytics": "^1.5.0",
         "@xmldom/xmldom": "^0.9.8",
         "ai": "^5.0.89",
         "base-64": "^1.0.0",