feat: decommission memoir-bot (CT 142)

Service was unused. Live steps (revoke SecondBrain deploy key, drop the Uptime
Kuma monitor, pct stop 142) were done 2026-09-02; pct destroy is deliberately
deferred a week.

- delete playbooks/pve-memoir-bot.yml.
- hosts.yml: drop the memoir-bot host and its monitoring_exporters entry.
- roles/monitoring_server/templates/prometheus.yml.j2: drop 192.168.1.26 target.
- roles/uptime_kuma/defaults: drop 192.168.1.26 from no_proxy.
- roles/lxc_docker_host/defaults: drop the memoir-bot extra-packages comment.

The registry entry, the ssh_config Host block and the status.yml unit list are
removed in the commits that also carry OpenTofu-migration / quorum changes to
those files.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012uoq5AVK8mkBgg83Mq6o5V

ansible/inventory/hosts.yml

@@ -64,10 +64,6 @@ all:
           ansible_host: 192.168.1.25
           expected_lan_ip: 192.168.1.25
 
-        memoir-bot:
-          ansible_host: 192.168.1.26
-          expected_lan_ip: 192.168.1.26
-
         mihomo:
           ansible_host: 192.168.1.27
           expected_lan_ip: 192.168.1.27
@@ -103,7 +99,6 @@ all:
         ovpn-mini:
         vaultwarden:
         gitea:
-        memoir-bot:
         mihomo:
         adguard:
         monitoring: