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/README.md

@@ -0,0 +1,37 @@
+# gemaal1
+
+Edge deployment for pumping station **Gemaal1** — first production site.
+
+## Hardware (fill in when provisioned)
+
+- Edge gateway model: ?
+- Plant LAN subnet: ?.?.?.0/24
+- WAN: ?
+- OT VLAN (PLC + OPCUA): ?.?.?.0/24
+- OPCUA endpoint: opc.tcp://?
+
+## What runs here
+
+nginx-proxy (plant-LAN-facing, certbot for TLS), wireguard-client (outbound tunnel to cloud), keycloak (local realm), portainer, influxdb (local DB), grafana (local SCADA), node-red, rabbitmq (general broker, internal only), postfix.
+
+## Run
+
+```bash
+cp .env.example .env     # fill in real secrets + PLANT_LAN_IP
+docker compose up -d
+docker compose ps
+```
+
+## Ingress
+
+| Port | Bound to |
+|---|---|
+| tcp/80, 443 | `${PLANT_LAN_IP}` only |
+
+Remote ops reach the same nginx via the WireGuard tunnel from cloud (no extra port published).
+
+## OT uplink
+
+Node-RED + EVOLV nodes talk to the OPCUA server on the OT VLAN. The edge gateway must have a NIC on that VLAN. OPCUA + PLC are **managed outside this repo**.
+
+See [`../../docs/architecture.md`](../../docs/architecture.md) for the full topology.