Add vercel.json to fix SPA routing for direct URL access

Co-authored-by: tonyqiu123 <90103972+tonyqiu123@users.noreply.github.com>

Author: 2 people

frontend/vercel.json

@@ -0,0 +1,8 @@
+{
+  "rewrites": [
+    {
+      "source": "/(.*)",
+      "destination": "/index.html"
+    }
+  ]
+}