Fix Vercel build configuration for output directory

vercel.json

@@ -1,29 +1,10 @@
 {
-  "version": 2,
-  "builds": [
-    {
-      "src": "api/**/*.py",
-      "use": "@vercel/python"
-    },
-    {
-      "src": "frontend/package.json",
-      "use": "@vercel/static-build",
-      "config": {
-        "distDir": "frontend/dist"
-      }
+  "buildCommand": "cd frontend && npm ci && npm run build",
+  "outputDirectory": "frontend/dist",
+  "installCommand": "pip install -r requirements.txt",
+  "functions": {
+    "api/**/*.py": {
+      "runtime": "python3.9"
     }
-  ],
-  "routes": [
-    {
-      "src": "/api/(.*)",
-      "dest": "/api/$1"
-    },
-    {
-      "src": "/(.*)",
-      "dest": "/frontend/$1"
-    }
-  ],
-  "env": {
-    "PYTHON_VERSION": "3.9"
   }
 }