docs: onboard AdGuard Home to Ansible; retire check-mx2; migrate plan to Linear

- Add dns.windy.lan to Ansible inventory (adguardhome group/profile) with a
  read-only healthcheck template, systemd timer, and on-demand report parity
  with the other active hosts; verified green on the host.
- Add synapse.chans.xyz to the AGENTS.md active-host quick map.
- Remove plans/; migrate decisions/verification to a Linear vps project doc and
  file the remaining gaps as W1N-46..49 with blocking edges.
- Retire scripts/check-mx2.sh; point mailcow health/update runbooks and the
  mx2 host file at the Ansible health report.
- Trim us2 stub software to verified running services; note dormant dirs.
- Normalize repo docs to English; drop the non-existent CONTEXT.md/ADR claim
  and remove docs/agents/domain.md.

inventory/hosts.md

@@ -21,6 +21,7 @@ diagnosis and procedures that are deliberately interactive or destructive; see
 | pgweb.wsvc.info | PowerDNS Postgres UI | — (HTTPS) | → hk2 | active | see hk2 |
 | **synapse.chans.xyz** | Matrix homeserver (ESS: Synapse + MAS + Element) | `ssh -4 windy@synapse.chans.xyz` | `169.58.86.13` | **active** | [hosts/synapse.chans.xyz.md](../hosts/synapse.chans.xyz.md) |
 | **gfw.windy.lan** | OpenWrt LAN gateway / OpenClash | `ssh -4 root@192.168.66.1` | `192.168.66.1` | **active** | [hosts/gfw.windy.lan.md](../hosts/gfw.windy.lan.md) |
+| **dns.windy.lan** | AdGuard Home LAN DNS + Mihomo explicit proxy | `ssh -4 windy@192.168.66.36` | `192.168.66.36` | **active** | [hosts/dns.windy.lan.md](../hosts/dns.windy.lan.md) |
 | **gw** | EdgeRouter X primary LAN gateway | `ssh -4 zhiqiang@192.168.66.254` | `192.168.66.254` | **active** | [hosts/gw.md](../hosts/gw.md) |
 | **ubnt** | UniFi Network Controller | `ssh -4 windy@192.168.66.46` | `192.168.66.46` | **active** | [hosts/ubnt.md](../hosts/ubnt.md) |