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/wireguard-client/README.md

@@ -0,0 +1,9 @@
+# wireguard-client
+
+VPN client running at each edge. **Edge-only stack.**
+
+- **Networks**: `app` + `mgmt` (so other edge containers can route through the tunnel)
+- **No published port** — initiates outbound to the cloud `wireguard-server` on `udp/51820`
+- **Config**: `config/wg0.conf` (per-site, contains the site's private key + cloud peer pubkey + AllowedIPs)
+- **Routing**: edge containers reach cloud-side services by routing destined-for-cloud-subnet traffic via this client
+- **TODO**: routing strategy (split-tunnel vs full), keepalive interval, MTU tuning per WAN type