docs(readme): document the mc-status server-status JSON endpoint

Describe the self-hosted mc-status pinger (mcstatus.io v2 JSON, same-origin via
caddy /api/mcstatus/* → mc-status:8080) that the landing ServerCard reads, with
the apex endpoint and a direct-to-caddy curl example.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -129,6 +129,32 @@ down" from "ingress/TLS/DNS down"; public-URL targets test the whole chain.
 `status` is in the default `LE_SUBDOMAINS`; the nginx vhost adds websocket
 upgrade headers for Kuma's live UI.
 
+## Server status JSON (mc-status)
+
+`mc-status` is a self-hosted SLP→JSON pinger (built from `docker/mc-status`, an
+mcutil wrapper) that the landing's `ServerCard` reads for live player count + MOTD.
+It emits **mcstatus.io v2** JSON, so the card consumes it unchanged — but
+same-origin, with no CORS and no third-party calls. caddy proxies the apex
+`/api/mcstatus/*` path to `mc-status:8080` (strips the prefix); the container has
+no published port. The pinger only ever probes its configured `MC_STATUS_TARGET`,
+so the path after the prefix is ignored.
+
+Endpoint (apex, same-origin):
+
+```
+https://${BASE_DOMAIN}/api/mcstatus/v2/status/java/${BASE_DOMAIN}
+```
+
+Hitting caddy directly (localhost-only, routes by Host header) — e.g. `ulicraft.net`
+on `127.0.0.1:8880`:
+
+```sh
+curl -H "Host: ulicraft.net" \
+  http://127.0.0.1:8880/api/mcstatus/v2/status/java/ulicraft.net
+```
+
+Wired in `landing/src/data/site.ts` (`statusApi`) and `caddy/conf.d/10-static.caddy`.
+
 ## Join (guests)
 
 1. Open `https://${BASE_DOMAIN}`, download FjordLauncherUnlocked for your OS.