feat: SQL=postgres, nginx+certbot, MQTT split, ML stacks, gitea HTTPS-only, gemaal1 site

Round-2 changes locking in scaffold-phase decisions and adding ML/notebook stacks.

Locked decisions
- sql: postgres 16-alpine (was TBD); init.d/ mount for per-app DB provisioning
- nginx-proxy: stock nginx + certbot sidecar (was nginx:alpine TODO).
  Chose stock over nginxproxy/nginx-proxy because stream{} is required for
  MQTT-TLS reverse-proxy on tcp/8883 to rabbitmq:1883.
- gitea: HTTPS-only (DISABLE_SSH=true). No SSH port published.

MQTT split
- Remove stacks/mqtt placeholder.
- Add stacks/rabbitmq — general-purpose broker (AMQP + MQTT plugin),
  used at both cloud and edge. External MQTT clients reach cloud broker
  via nginx stream-proxy on 8883.
- Add stacks/mosquitto — reserved for the FROST (SensorThings) stack
  only. Cloud-only. Internal to its own stack; no external ingress.

ML / notebooks (cloud-only)
- stacks/mlflow — experiment tracking + model registry. Postgres backend
  on sql stack; local volume for artifacts (S3/MinIO is a TODO).
- stacks/jupyterhub — multi-user notebook server. DockerSpawner via
  mounted docker.sock; users spawn into cloud-app network so they can
  reach mlflow, influxdb (via grafana), rabbitmq.

Sites
- sites/gemaal1 — first edge deployment scaffold. Site-local override
  template for binding nginx to PLANT_LAN_IP.

Docs
- README + docs/architecture.md updated: stacks table now lists 15 stacks,
  ingress + attachment tables reflect mlflow/jupyterhub, TLS strategy
  section locked, MQTT-split section added, Gitea HTTPS-only noted.

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

sites/gemaal1/.env.example

@@ -0,0 +1,32 @@
+TZ=Europe/Amsterdam
+
+# Plant LAN interface IP that nginx-proxy binds to (replaces 0.0.0.0)
+PLANT_LAN_IP=
+
+# WireGuard client peer config: see stacks/wireguard-client/config/wg0.conf
+
+# InfluxDB (local DB at this plant)
+INFLUX_ADMIN_USER=admin
+INFLUX_ADMIN_PASSWORD=
+INFLUX_ADMIN_TOKEN=
+INFLUX_ORG=wbd
+INFLUX_BUCKET=gemaal1
+
+# Grafana (local SCADA at this plant)
+GRAFANA_ADMIN_USER=admin
+GRAFANA_ADMIN_PASSWORD=
+GRAFANA_ROOT_URL=
+
+# Keycloak (local realm)
+KEYCLOAK_ADMIN=admin
+KEYCLOAK_ADMIN_PASSWORD=
+KEYCLOAK_HOSTNAME=
+
+# RabbitMQ (general broker, edge-local — internal only)
+RABBITMQ_USER=admin
+RABBITMQ_PASSWORD=
+RABBITMQ_VHOST=gemaal1
+
+# Postfix
+POSTFIX_RELAYHOST=
+POSTFIX_FROM_DOMAIN=