feat: add Docker infrastructure for 8-node cluster topology (2 central + 3 sites)

Multi-stage Dockerfile with NuGet restore layer caching, per-node appsettings
with Docker hostnames, shared bridge network with infra services, and
build/deploy/teardown scripts. Ports use 90xx block to avoid conflicts.

docker/docker-compose.yml

@@ -0,0 +1,126 @@
+services:
+  central-a:
+    image: scadalink:latest
+    container_name: scadalink-central-a
+    environment:
+      SCADALINK_CONFIG: Central
+      ASPNETCORE_URLS: "http://+:5000"
+    ports:
+      - "9001:5000"   # Web UI + Inbound API
+      - "9011:8081"   # Akka remoting (host access for CLI/debugging)
+    volumes:
+      - ./central-node-a/appsettings.Central.json:/app/appsettings.Central.json:ro
+      - ./central-node-a/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+  central-b:
+    image: scadalink:latest
+    container_name: scadalink-central-b
+    environment:
+      SCADALINK_CONFIG: Central
+      ASPNETCORE_URLS: "http://+:5000"
+    ports:
+      - "9002:5000"   # Web UI + Inbound API
+      - "9012:8081"   # Akka remoting
+    volumes:
+      - ./central-node-b/appsettings.Central.json:/app/appsettings.Central.json:ro
+      - ./central-node-b/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+  site-a-a:
+    image: scadalink:latest
+    container_name: scadalink-site-a-a
+    environment:
+      SCADALINK_CONFIG: Site
+    ports:
+      - "9021:8082"   # Akka remoting (host access for debugging)
+    volumes:
+      - ./site-a-node-a/appsettings.Site.json:/app/appsettings.Site.json:ro
+      - ./site-a-node-a/data:/app/data
+      - ./site-a-node-a/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+  site-a-b:
+    image: scadalink:latest
+    container_name: scadalink-site-a-b
+    environment:
+      SCADALINK_CONFIG: Site
+    ports:
+      - "9022:8082"   # Akka remoting
+    volumes:
+      - ./site-a-node-b/appsettings.Site.json:/app/appsettings.Site.json:ro
+      - ./site-a-node-b/data:/app/data
+      - ./site-a-node-b/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+  site-b-a:
+    image: scadalink:latest
+    container_name: scadalink-site-b-a
+    environment:
+      SCADALINK_CONFIG: Site
+    ports:
+      - "9031:8082"   # Akka remoting
+    volumes:
+      - ./site-b-node-a/appsettings.Site.json:/app/appsettings.Site.json:ro
+      - ./site-b-node-a/data:/app/data
+      - ./site-b-node-a/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+  site-b-b:
+    image: scadalink:latest
+    container_name: scadalink-site-b-b
+    environment:
+      SCADALINK_CONFIG: Site
+    ports:
+      - "9032:8082"   # Akka remoting
+    volumes:
+      - ./site-b-node-b/appsettings.Site.json:/app/appsettings.Site.json:ro
+      - ./site-b-node-b/data:/app/data
+      - ./site-b-node-b/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+  site-c-a:
+    image: scadalink:latest
+    container_name: scadalink-site-c-a
+    environment:
+      SCADALINK_CONFIG: Site
+    ports:
+      - "9041:8082"   # Akka remoting
+    volumes:
+      - ./site-c-node-a/appsettings.Site.json:/app/appsettings.Site.json:ro
+      - ./site-c-node-a/data:/app/data
+      - ./site-c-node-a/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+  site-c-b:
+    image: scadalink:latest
+    container_name: scadalink-site-c-b
+    environment:
+      SCADALINK_CONFIG: Site
+    ports:
+      - "9042:8082"   # Akka remoting
+    volumes:
+      - ./site-c-node-b/appsettings.Site.json:/app/appsettings.Site.json:ro
+      - ./site-c-node-b/data:/app/data
+      - ./site-c-node-b/logs:/app/logs
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
+networks:
+  scadalink-net:
+    external: true