refactor(dns): rename frost.wbd-rd.nl → sta.wbd-rd.nl; drop redundant portainer.wbd-rd.nl

Match the short-functional naming convention used by the other vhosts
(git, auth, dash, flow, ml, hub, ops, mq, ci, mqtt). FROST implements
OGC SensorThings API, so `sta` is the natural fit.

portainer.wbd-rd.nl is dropped from deploy.sh HOSTS — there is no
nginx vhost for it; portainer is already served via ops.wbd-rd.nl.

DNS prereq for first deploy is now: create one new A record for
sta.wbd-rd.nl → cloud public IP. All other short subdomains already
point correctly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

stacks/frost/README.md

@@ -2,7 +2,7 @@
 
 [FROST-Server](https://github.com/FraunhoferIOSB/FROST-Server) — an OGC SensorThings API server. Stores sensors, observations, datastreams in postgis; exposes REST + MQTT.
 
-- **Public hostname**: `frost.wbd-rd.nl`
+- **Public hostname**: `sta.wbd-rd.nl`
   - `/FROST-Server` → REST + admin UI (frost-http:8080)
   - `/mqtt`         → WebSocket MQTT for SensorThings clients (frost-mqtt:9876)
 - **Networks**: `frost-internal` (private bus) + `app` (nginx ingress)