fix: map outline hostname to Tailscale IP of domverse

outline-sync runs on domverse-berlin and connects to Outline on domverse.de
via Tailscale. Docker DNS does not cross hosts, so map the hostname via
extra_hosts to the Tailscale IP 100.104.53.109.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -43,6 +43,8 @@ services:
     environment:
       - OUTLINE_URL=${OUTLINE_URL:-http://outline:3000}
       - OUTLINE_TOKEN=${OUTLINE_TOKEN}
+    extra_hosts:
+      - "outline:100.104.53.109"
 
 volumes:
   tailscale-state: