Fix Discord activity page not loading by adjusting Vercel routing

Add a host-based rewrite in vercel.json to handle requests originating from Discord's proxy, ensuring the Activity page loads correctly.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 9203795e-937a-4306-b81d-b4d5c78c240e
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Event-Id: 6ccd8b82-c530-443f-95c3-e82995a96239
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/7c94b7a0-29c7-4f2e-94ef-44b2153872b7/9203795e-937a-4306-b81d-b4d5c78c240e/qPXTzuE
Replit-Helium-Checkpoint-Created: true

vercel.json

@@ -58,6 +58,11 @@
     }
   ],
   "rewrites": [
+    {
+      "source": "/:path(.*)",
+      "has": [{ "type": "host", "value": "(?<proxy>.+)\\.discordsays\\.com" }],
+      "destination": "/index.html"
+    },
     {
       "source": "/:path(.*)",
       "has": [{ "type": "host", "value": "(?<sub>.+)\\.aethex\\.me" }],