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/.env.example

@@ -1,5 +1,4 @@
 GITEA_ROOT_URL=
-GITEA_DB_TYPE=postgres
 GITEA_DB_HOST=sql:5432
 GITEA_DB_NAME=gitea
 GITEA_DB_USER=gitea

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

stacks/gitea/compose.yml

@@ -1,5 +1,6 @@
 # gitea — git server (cloud only)
 # Networks: app + data (uses sql stack as DB backend)
+# Ingress: HTTPS-only via nginx-proxy. No SSH port published.
 
 services:
   gitea:
@@ -10,7 +11,8 @@ services:
       USER_UID: "1000"
       USER_GID: "1000"
       GITEA__server__ROOT_URL: ${GITEA_ROOT_URL}
-      GITEA__database__DB_TYPE: ${GITEA_DB_TYPE:-postgres}
+      GITEA__server__DISABLE_SSH: "true"
+      GITEA__database__DB_TYPE: postgres
       GITEA__database__HOST: ${GITEA_DB_HOST:-sql:5432}
       GITEA__database__NAME: ${GITEA_DB_NAME:-gitea}
       GITEA__database__USER: ${GITEA_DB_USER}
@@ -18,7 +20,6 @@ services:
       TZ: ${TZ:-Europe/Amsterdam}
     volumes:
       - gitea-data:/data
-    # SSH port: TODO — decide if Gitea SSH (22/2222) is exposed via nginx stream or skipped
 
 networks:
   app: