Fix playbook bugs from review, add Telegram alerts to health and service checks

Review fixes:
- Availability plays: "ping_result is succeeded" is true for unreachable
  hosts, so offline hosts were added to reachable_hosts and failed the
  next play. Test reachability explicitly (7 playbooks).
- bootstrap_lxc: vim-enhanced and mtr-tiny package names, enable CRB next
  to EPEL, add the root key without replacing authorized_keys, validate
  sshd_config edits and restart sshd only on change.
- backup_docker: the command module does not expand $(...); fix rsync
  filter order and add --exclude=*; restart only the containers that were
  stopped, even when rsync fails; read the storage address from the
  inventory; keep semaphore and semaphore-db running.
- new_lxc: community.general.proxmox no longer exists, use
  community.proxmox; node is mini-pc; valid hostname; password or token
  auth; let the module pick the VMID; longer timeout.
- proxmox-backup: surface the vzdump exit code, let vzdump prune with
  keep-last, drop the rename/prune steps that globbed *.zstd.
- time-region: chrony regex no longer comments out its own server line;
  /etc/localtime as a symlink; reuse facts across plays.
- update_pihole_blocklists: FQCN, become: true, changed_when.
- ansible.cfg gathering = smart; update_system only pings ubuntu/rocky.

Telegram alerts:
- health_check: filesystems above disk_warn_pct (default 80), excluding
  efivarfs, and offline hosts.
- service_check: services not running.
- One message per run from localhost, credentials from Semaphore
  (TELEGRAM_BOT_TOKEN / TELEGRAM_CHAT_ID), no_log on the send task,
  prints the alert text when Telegram is not configured.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XEizHawueRXUcxQELRZ8kq

playbooks/reboot_check.yml

@@ -22,12 +22,12 @@
     - name: Add reachable hosts to group
       ansible.builtin.group_by:
         key: reachable_hosts
-      when: ping_result is succeeded
+      when: ping_result is reachable and ping_result is succeeded
 
     - name: Report offline hosts
       ansible.builtin.debug:
         msg: "{{ inventory_hostname }} - OFFLINE"
-      when: ping_result is not succeeded
+      when: ping_result is unreachable or ping_result is failed
       delegate_to: localhost
 
 - name: Reboot Check - Ubuntu