fix: remove user-agent restriction from article OG rewrite

All /a/:naddr requests now route to article-og handler, which handles crawler detection internally. This ensures social media crawlers always receive proper OpenGraph meta tags.

vercel.json

@@ -2,13 +2,6 @@
   "rewrites": [
     {
       "source": "/a/:naddr",
-      "has": [
-        {
-          "type": "header",
-          "key": "user-agent",
-          "value": ".*(bot|crawl|spider|slurp|facebook|twitter|linkedin|whatsapp|telegram|slack|discord|preview).*"
-        }
-      ],
       "destination": "/api/article-og?naddr=:naddr"
     },
     {