feat(seo): add Signal to bot detection list

🤖 Generated with [Claude Code](https://claude.ai/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: MarkusNeusinger

app/nginx.conf

@@ -7,6 +7,7 @@ map $http_user_agent $is_bot {
     ~*slackbot 1;
     ~*telegrambot 1;
     ~*whatsapp 1;
+    ~*signal 1;
     ~*googlebot 1;
     ~*bingbot 1;
     ~*discordbot 1;