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/keycloak/compose.yml

@@ -0,0 +1,25 @@
+# keycloak — identity / SSO
+# Networks: app (apps reach the realm endpoints) + mgmt (admin console)
+
+services:
+  keycloak:
+    image: quay.io/keycloak/keycloak:26.0
+    restart: unless-stopped
+    command: ["start", "--optimized"]
+    networks: [app, mgmt]
+    environment:
+      KC_BOOTSTRAP_ADMIN_USERNAME: ${KEYCLOAK_ADMIN}
+      KC_BOOTSTRAP_ADMIN_PASSWORD: ${KEYCLOAK_ADMIN_PASSWORD}
+      KC_HOSTNAME: ${KEYCLOAK_HOSTNAME:-}
+      KC_PROXY_HEADERS: xforwarded
+      KC_HTTP_ENABLED: "true"
+      # TODO: external DB (KC_DB=postgres) once sql stack lands
+    volumes:
+      - keycloak-data:/opt/keycloak/data
+
+networks:
+  app:
+  mgmt:
+
+volumes:
+  keycloak-data: