Add simple test page for 404 debugging

- Create simple.html as fallback test page
- Set root route to simple.html for immediate access
- Include API test functionality in the page
- Verify basic Vercel deployment works

vercel.json

@@ -1,6 +1,10 @@
 {
   "version": 2,
   "routes": [
+    {
+      "src": "/simple",
+      "dest": "/simple.html"
+    },
     {
       "src": "/api/test",
       "dest": "/api/test.js"
@@ -14,7 +18,7 @@
       "dest": "/api/files.js"
     },
     {
-      "src": "/(.*\\.(css|js|json|svg|png|jpg|jpeg|gif|ico|woff|woff2|ttf|eot))",
+      "src": "/(.*\\.(css|js|json|svg|png|jpg|jpeg|gif|ico|woff|woff2|ttf|eot|html))",
       "dest": "/$1"
     },
     {
@@ -22,8 +26,8 @@
       "dest": "/admin/$1"
     },
     {
-      "src": "/(.*)",
-      "dest": "/index.html"
+      "src": "/",
+      "dest": "/simple.html"
     }
   ]
 }