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/compose.yml

@@ -0,0 +1,23 @@
+# wireguard-client — VPN client (edge only)
+# Networks: app + mgmt
+# No published port — initiates outbound to cloud server
+
+services:
+  wireguard-client:
+    image: linuxserver/wireguard:latest
+    restart: unless-stopped
+    cap_add: [NET_ADMIN, SYS_MODULE]
+    sysctls:
+      - net.ipv4.conf.all.src_valid_mark=1
+    networks: [app, mgmt]
+    environment:
+      PUID: "1000"
+      PGID: "1000"
+      TZ: ${TZ:-Europe/Amsterdam}
+    volumes:
+      - ./config/wg0.conf:/config/wg_confs/wg0.conf:ro
+      - /lib/modules:/lib/modules:ro
+
+networks:
+  app:
+  mgmt: