Fix serverless functions: simplify API structure

- Replace complex Express-style handler with simple module.exports
- Add separate API endpoints for better organization
- Simplify vercel.json routing configuration
- Remove ES modules to use CommonJS for Vercel compatibility
- Add dedicated test API endpoint for debugging

vercel.json

@@ -1,59 +1,29 @@
 {
   "version": 2,
-  "builds": [
-    {
-      "src": "api/simple.js",
-      "use": "@vercel/node"
-    }
-  ],
   "routes": [
     {
-      "src": "/api/(.*)",
-      "dest": "/api/simple.js"
+      "src": "/api/test",
+      "dest": "/api/test.js"
     },
     {
-      "src": "/health",
-      "dest": "/api/simple.js"
+      "src": "/api/files/public",
+      "dest": "/api/files.js"
     },
     {
-      "src": "/(.*\\.(css|js|json|svg|png|jpg|jpeg|gif|ico|woff|woff2|ttf|eot|html))",
-      "headers": {
-        "Cache-Control": "public, max-age=31536000, immutable"
-      },
+      "src": "/api/files",
+      "dest": "/api/files.js"
+    },
+    {
+      "src": "/(.*\\.(css|js|json|svg|png|jpg|jpeg|gif|ico|woff|woff2|ttf|eot))",
       "dest": "/$1"
     },
-    {
-      "src": "/index\\.html",
-      "headers": {
-        "Cache-Control": "public, max-age=0, must-revalidate"
-      },
-      "dest": "/index.html"
-    },
     {
       "src": "/admin/(.*)",
       "dest": "/admin/$1"
     },
-    {
-      "src": "^/$",
-      "dest": "/api/simple.js"
-    },
     {
       "src": "/(.*)",
       "dest": "/index.html"
     }
-  ],
-  "headers": [
-    {
-      "source": "/api/(.*)",
-      "headers": [
-        {
-          "key": "Cache-Control",
-          "value": "public, max-age=0, s-maxage=86400"
-        }
-      ]
-    }
-  ],
-  "env": {
-    "NODE_ENV": "production"
-  }
+  ]
 }