Adds tools/pve/post-install-hook-examples.sh — a single, well-commented
file that demonstrates how to use the new var_post_install hook.
It is NOT meant to be executed directly. Each example sits between clear
BEGIN/END markers; users copy the block they want into their own .sh on
the Proxmox host and point var_post_install at it.
Examples:
1. minimal-logger.sh — append every new LXC to a CSV log
2. discord-gotify-notify.sh — Discord embed + Gotify push
3. auto-pool-tags-backup.sh — pool, tags, pi-hole DNS, vzdump
4. inject-ssh-and-monitoring.sh— admin SSH key, Beszel agent, Uptime-Kuma
5. per-app-router.sh — dispatcher with per-NSAPP behavior
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