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

vercel.json

@@ -0,0 +1,12 @@
+{
+    "functions": {
+        "app/api/chat/route.ts": {
+            "memory": 512,
+            "maxDuration": 120
+        },
+        "app/api/**/route.ts": {
+            "memory": 256,
+            "maxDuration": 10
+        }
+    }
+}