feat(status): Uptime Kuma monitoring at status.${BASE_DOMAIN}

Add docker-compose.status.yml (louislam/uptime-kuma) layered on the caddy
ingress, joining mcnet so it probes the stack by internal service name and
the public vhosts end-to-end. Host port bound to 127.0.0.1:3001 only; public
access via nginx -> caddy.

- caddy/conf.d/50-status.caddy: status. -> uptime-kuma:3001
- nginx caddy-front template: status. TLS vhost + websocket upgrade headers
  for Kuma's live UI; status. added to the HTTP->HTTPS redirect list
- status added to LE_SUBDOMAINS defaults (.env.example, issue-letsencrypt.sh)
- README: Status monitoring section + recommended monitor list (incl. native
  Minecraft-protocol ping)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.env.example

@@ -37,7 +37,7 @@ DISTRIBUTION_WEB_ROOT=/home/oier/projects/mc-mods/ulicraft-group/ulicraft-distri
 # Only needed to issue real TLS certs. DNS-01 needs no inbound ports.
 LE_EMAIL=you@example.com
 # space-separated subdomains; apex ${BASE_DOMAIN} is always included
-LE_SUBDOMAINS=auth pack distribution www avatar
+LE_SUBDOMAINS=auth pack distribution www avatar status
 # OVH API creds (DNS zone write). Create at https://eu.api.ovh.com/createToken/
 # OVH_CK can be blank on first run — acme.sh prints an auth URL, then paste it.
 OVH_END_POINT=ovh-eu