feat: external HTTPS monitoring pull via monitor.php

Add cron-ready pull checks for critical URLs with SSL expiry warnings,
retry-before-alert, JSON results in private/data, email alerts, and a
90-day target-list review reminder.

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

server.env.example

@@ -16,6 +16,7 @@ SMTP_FROM=monitor@0012.de
 ALERT_EMAIL=
 
 # Monitoring
+TARGETS_REVIEW_INTERVAL_DAYS=90
 MONITOR_INGEST_TOKEN=
 MONITOR_INGEST_URL=https://0012.de/ingest.php