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.

src/ScadaLink.ManagementService/ManagementActor.cs

@@ -13,6 +13,7 @@ using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Messages.Management;
 using ScadaLink.DeploymentManager;
 using ScadaLink.HealthMonitoring;
+using ScadaLink.Communication;
 using ScadaLink.TemplateEngine;
 using ScadaLink.TemplateEngine.Services;
 
@@ -320,9 +321,16 @@ public class ManagementActor : ReceiveActor
     private static async Task<object?> HandleCreateSite(IServiceProvider sp, CreateSiteCommand cmd)
     {
         var repo = sp.GetRequiredService<ISiteRepository>();
-        var site = new Site(cmd.Name, cmd.SiteIdentifier) { Description = cmd.Description };
+        var site = new Site(cmd.Name, cmd.SiteIdentifier)
+        {
+            Description = cmd.Description,
+            NodeAAddress = cmd.NodeAAddress,
+            NodeBAddress = cmd.NodeBAddress
+        };
         await repo.AddSiteAsync(site);
         await repo.SaveChangesAsync();
+        var commService = sp.GetService<CommunicationService>();
+        commService?.RefreshSiteAddresses();
         return site;
     }
 
@@ -333,8 +341,12 @@ public class ManagementActor : ReceiveActor
             ?? throw new InvalidOperationException($"Site with ID {cmd.SiteId} not found.");
         site.Name = cmd.Name;
         site.Description = cmd.Description;
+        site.NodeAAddress = cmd.NodeAAddress;
+        site.NodeBAddress = cmd.NodeBAddress;
         await repo.UpdateSiteAsync(site);
         await repo.SaveChangesAsync();
+        var commService = sp.GetService<CommunicationService>();
+        commService?.RefreshSiteAddresses();
         return site;
     }
 
@@ -348,6 +360,8 @@ public class ManagementActor : ReceiveActor
                 $"Cannot delete site {cmd.SiteId}: it has {instances.Count} instance(s).");
         await repo.DeleteSiteAsync(cmd.SiteId);
         await repo.SaveChangesAsync();
+        var commService = sp.GetService<CommunicationService>();
+        commService?.RefreshSiteAddresses();
         return true;
     }