Update architecture and backup documentation to include Healthchecks integration

Add Healthchecks service details to architecture and backup documentation, including its role as a Dead man's switch for backups. Update backup scripts to utilize systemd timers instead of cron for improved scheduling. Enhance network topology documentation to reflect Healthchecks integration in the VPS Miran setup. This update clarifies backup processes and enhances overall system reliability.

scripts/systemd/README.md

@@ -0,0 +1,24 @@
+# Systemd unit-файлы для бэкапов и мониторинга
+
+Копировать на хост Proxmox в `/etc/systemd/system/`:
+
+```bash
+cp *.service *.timer /etc/systemd/system/
+systemctl daemon-reload
+```
+
+Включить все таймеры:
+
+```bash
+for t in backup-*.timer notify-vzdump-success.timer verify-*.timer backup-watchdog-timers.timer backup-healthcheck-ping.timer; do
+  systemctl enable --now "$t" 2>/dev/null || true
+done
+```
+
+Проверка:
+
+```bash
+systemctl list-timers --all | grep backup
+```
+
+Перед миграцией с cron — отключить задания в crontab (`crontab -e`).