scaffold: hub-and-spoke layout, 4-network topology, 13 stack stubs

Initial structure for R&D infrastructure:

- stacks/ — 13 reusable, runnable stack stubs (kebab-case)
  cloud-and-edge: node-red, influxdb, grafana, keycloak, portainer,
                  nginx-proxy, mqtt, postfix
  cloud-only:     wireguard-server, gitea, jenkins, sql (postgres stub)
  edge-only:      wireguard-client

- cloud/ — single central hub composition with 4 networks
           (edge, app, data internal, mgmt) and include: stubs
- sites/ — per-plant edge folders (template README only for now)
- docs/architecture.md — hub-and-spoke + ingress + segmentation rationale

Network model: only nginx-proxy (80/443/8883) and wireguard-server
(51820/udp) publish ports on the cloud host. Edge nginx publishes
80/443 on plant-LAN interface only. MQTT cloud-side via nginx stream
proxy; MQTT edge-side internal-only; Postfix outbound-only.

OT layer (OPCUA, PLCs) is out of scope for this repo.

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

stacks/nginx-proxy/README.md

@@ -0,0 +1,12 @@
+# nginx-proxy
+
+The single web ingress. Reverse-proxies HTTPS UIs and stream-proxies MQTT-TLS.
+
+- **Networks**: `edge` (the only port-publisher) + `app` (talks to upstream services)
+- **Host ports**: `tcp/80`, `tcp/443`, `tcp/8883`
+- **Config**:
+  - `config/nginx.conf` — base
+  - `config/conf.d/*.conf` — HTTP vhosts (one per upstream UI)
+  - `config/stream.d/mqtt.conf` — MQTT-TLS stream block, SNI route to mqtt broker
+  - `config/certs/` — TLS certs (volume-mounted from cert manager)
+- **TODO**: pick SSL strategy (acme-companion sidecar vs certbot vs internal PKI), write vhost templates per upstream