chore: add vercel.json for clean URLs and SPA fallback routing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Thunnini

docs/vercel.json

@@ -0,0 +1,7 @@
+{
+  "cleanUrls": true,
+  "trailingSlash": false,
+  "rewrites": [
+    { "source": "/(.*)", "destination": "/index.html" }
+  ]
+}