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-server/README.md

@@ -0,0 +1,9 @@
+# wireguard-server
+
+VPN ingress for edges and remote ops. **Cloud-only stack.**
+
+- **Networks**: `edge` (the only non-nginx public ingress) + `mgmt` (admin access into tunnel)
+- **Host port**: `udp/51820`
+- **Why not behind nginx?** WireGuard is connectionless UDP with crypto-routed packets; proxying it through nginx-stream breaks NAT/MTU and adds no security benefit. It publishes its port directly.
+- **Peers**: managed via `wg-server-config/peer_*` config files. Each edge gets one peer.
+- **TODO**: peer onboarding workflow, AllowedIPs split-tunnel decisions per peer