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/Dockerfile

@@ -30,7 +30,7 @@ RUN dotnet restore src/ScadaLink.Host/ScadaLink.Host.csproj
 FROM restore AS build
 COPY src/ src/
 RUN dotnet publish src/ScadaLink.Host/ScadaLink.Host.csproj \
-    -c Release -o /app/publish --no-restore
+    -c Release -o /app/publish
 
 # Stage 3: Runtime (minimal image, no SDK)
 FROM mcr.microsoft.com/dotnet/aspnet:10.0 AS runtime