seedbox: fix qbittorrent healthcheck

qBittorrent has no /health endpoint (404) and its WebAPI requires
authentication (403), so probe the WebUI root instead.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NMEYncwy1yEBJCSb8HLgXg

cookbooks/seedbox/qbittorrent.container

@@ -31,7 +31,7 @@ Entrypoint=/app/qbittorrent-nox
 Exec=--webui-port=8080
 
 # Health check
-HealthCmd=curl -f http://127.0.0.1:8080/health
+HealthCmd=curl -f http://127.0.0.1:8080/
 HealthInterval=30s
 HealthTimeout=10s
 HealthStartPeriod=30s