revert: 移除 CONN_HEALTH_CHECKS（远程库每条请求多打一次 SQL）；加可选慢请求追踪

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy/apply-lag-fix.sh

@@ -16,14 +16,6 @@ sleep 2
 systemctl is-active gunicorn-dianjing.service
 pgrep -cf 'gunicorn.*a_long_dianjing' || true
 
-echo ""
-echo ">>> 安装 worker 保活 cron（空闲后不卡）"
-chmod +x deploy/gunicorn-warmup.sh
-cp deploy/gunicorn-warmup.cron /etc/cron.d/gunicorn-warmup
-chmod 644 /etc/cron.d/gunicorn-warmup
-bash deploy/gunicorn-warmup.sh
-echo "  cron 已安装，每2分钟预热 worker"
-
 echo ""
 echo ">>> 最近慢请求 (rt>=0.5s):"
 grep -a 'hqhd' "$NGINX_LOG" | awk 'match($0,/rt=([0-9.]+)/,a){if(a[1]+0>=0.5)print}' | tail -5