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/compose.yml

@@ -0,0 +1,40 @@
+# Edge deployment for pumping station "Gemaal1".
+# First production site; template for additional plants.
+# Run: cp .env.example .env  &&  docker compose up -d
+
+name: edge-gemaal1
+
+# Uncomment as each stack is hardened beyond stub.
+include:
+  # - ../../stacks/nginx-proxy/compose.yml
+  # - ../../stacks/wireguard-client/compose.yml
+  # - ../../stacks/keycloak/compose.yml
+  # - ../../stacks/portainer/compose.yml
+  # - ../../stacks/influxdb/compose.yml
+  # - ../../stacks/grafana/compose.yml
+  # - ../../stacks/node-red/compose.yml
+  # - ../../stacks/rabbitmq/compose.yml
+  # - ../../stacks/postfix/compose.yml
+
+# Site-specific overrides — bind nginx to the plant-LAN interface only.
+# Uncomment once nginx-proxy is wired up and PLANT_LAN_IP is set in .env.
+# services:
+#   nginx:
+#     ports:
+#       - "${PLANT_LAN_IP}:80:80"
+#       - "${PLANT_LAN_IP}:443:443"
+
+networks:
+  edge:
+    name: edge-gemaal1-edge
+    driver: bridge
+  app:
+    name: edge-gemaal1-app
+    driver: bridge
+  data:
+    name: edge-gemaal1-data
+    driver: bridge
+    internal: true
+  mgmt:
+    name: edge-gemaal1-mgmt
+    driver: bridge