feat: replace site registration with database-driven site addressing

Central now resolves site Akka remoting addresses from the Sites DB table
(NodeAAddress/NodeBAddress) instead of relying on runtime RegisterSite
messages. Eliminates the race condition where sites starting before central
had their registration dead-lettered. Addresses are cached in
CentralCommunicationActor with 60s periodic refresh and on-demand refresh
when sites are added/edited/deleted via UI or CLI.

docker/docker-compose.yml

@@ -4,6 +4,7 @@ services:
     container_name: scadalink-central-a
     environment:
       SCADALINK_CONFIG: Central
+      ASPNETCORE_ENVIRONMENT: Development
       ASPNETCORE_URLS: "http://+:5000"
     ports:
       - "9001:5000"   # Web UI + Inbound API
@@ -20,6 +21,7 @@ services:
     container_name: scadalink-central-b
     environment:
       SCADALINK_CONFIG: Central
+      ASPNETCORE_ENVIRONMENT: Development
       ASPNETCORE_URLS: "http://+:5000"
     ports:
       - "9002:5000"   # Web UI + Inbound API