Simplify Vercel configuration to fix frontend build handling

Remove builds array from vercel.json to resolve the warning:
"Due to builds existing in your configuration file, the Build and
Development Settings defined in your Project Settings will not apply"

This allows Vercel to properly handle frontend build deployment
and use the buildCommand to copy frontend/build to backend/.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: robdimarco-atxp

vercel.json

@@ -1,24 +1,10 @@
 {
   "version": 2,
-  "builds": [
-    {
-      "src": "backend/server.ts",
-      "use": "@vercel/node",
-      "config": {
-        "maxLambdaSize": "50mb",
-        "runtime": "nodejs20.x"
-      }
-    }
-  ],
-  "routes": [
-    {
-      "src": "/(.*)",
-      "dest": "/backend/server.ts"
-    }
-  ],
   "installCommand": "npm run install-all",
   "buildCommand": "npm run build && cp -r frontend/build backend/",
-  "env": {
-    "NODE_ENV": "production"
+  "functions": {
+    "backend/dist/server.js": {
+      "runtime": "nodejs20.x"
+    }
   }
 }