Add vercel.json: static SPA routing for Vercel deployment

vercel.json

@@ -0,0 +1,17 @@
+{
+  "cleanUrls": true,
+  "trailingSlash": false,
+  "rewrites": [
+    { "source": "/(.*)", "destination": "/index.html" }
+  ],
+  "headers": [
+    {
+      "source": "/(.*)",
+      "headers": [
+        { "key": "X-Content-Type-Options", "value": "nosniff" },
+        { "key": "X-Frame-Options", "value": "SAMEORIGIN" },
+        { "key": "Referrer-Policy", "value": "strict-origin-when-cross-origin" }
+      ]
+    }
+  ]
+}