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>

stacks/gitea/README.md

@@ -1,7 +1,8 @@
 # gitea
 
-Self-hosted git server. **Cloud-only stack.** (External repos live at `gitea.wbd-rd.nl`; this is for R&D internal use.)
+Self-hosted git server. **Cloud-only.** (External repos live at `gitea.wbd-rd.nl`; this is for R&D internal use.)
 
-- **Networks**: `app` (UI) + `data` (DB backend in `sql` stack)
+- **Networks**: `app` (UI) + `data` (postgres backend in `sql` stack)
 - **Volume**: `gitea-data` (repos + LFS + actions runners)
-- **TODO**: SSH access strategy (nginx stream proxy port 22, or skip and use HTTPS-only), Keycloak OIDC, runners for Gitea Actions
+- **SSH ingress**: **disabled** (`DISABLE_SSH=true`). All clones over HTTPS via nginx-proxy. Re-evaluate only if Gitea Actions runners need SSH push semantics.
+- **TODO**: Keycloak OIDC, Gitea Actions runners, LFS storage policy