Fix Vercel API routing configuration

🔧 Routing Fix:
- Remove redundant API rewrite rule that was causing conflicts
- Use negative lookahead regex to exclude API routes from frontend rewrites
- Only rewrite non-API, non-static routes to index.html
- This should resolve API endpoints returning HTML instead of JSON

🚀 Expected Result:
- /api/* routes will now properly reach Vercel functions
- Frontend routes will still work correctly
- Static assets remain unaffected

vercel.json

@@ -1,11 +1,7 @@
 {
   "rewrites": [
     {
-      "source": "/api/(.*)",
-      "destination": "/api/$1"
-    },
-    {
-      "source": "/(.*)",
+      "source": "/((?!api|static|_next).*)",
       "destination": "/index.html"
     }
   ],