Block /growth/ and /.agents/ with redirects, not rewrites

Vercel serves an existing static file before applying a rewrite, so the
previous rewrite block did nothing and the strategy docs returned 200.
Redirects run before the filesystem check, so these now leave the site.

vercel.json

@@ -5,6 +5,8 @@
   "trailingSlash": true,
   "cleanUrls": true,
   "redirects": [
+    { "source": "/.agents/:path*", "destination": "/404.html", "permanent": false },
+    { "source": "/growth/:path*", "destination": "/404.html", "permanent": false },
     {
       "source": "/en/index.html",
       "destination": "/en/",
@@ -251,10 +253,6 @@
       "permanent": true
     }
   ],
-  "rewrites": [
-    { "source": "/.agents/:path*", "destination": "/__internal-only" },
-    { "source": "/growth/:path*", "destination": "/__internal-only" }
-  ],
   "headers": [
     {
       "source": "/(.*)",