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.Host/Actors/AkkaHostedService.cs

@@ -169,7 +169,7 @@ akka {{
     private void RegisterCentralActors()
     {
         var centralCommActor = _actorSystem!.ActorOf(
-            Props.Create(() => new CentralCommunicationActor()),
+            Props.Create(() => new CentralCommunicationActor(_serviceProvider)),
             "central-communication");
 
         // Wire up the CommunicationService with the actor reference
@@ -264,13 +264,8 @@ akka {{
             var siteCommActor = _actorSystem.ActorSelection("/user/site-communication");
             siteCommActor.Tell(new RegisterCentralPath(_communicationOptions.CentralActorPath));
 
-            // Also register this site with Central so it knows our address
-            var centralSelection = _actorSystem.ActorSelection(_communicationOptions.CentralActorPath);
-            var localSiteCommPath = $"akka.tcp://scadalink@{_nodeOptions.NodeHostname}:{_nodeOptions.RemotingPort}/user/site-communication";
-            centralSelection.Tell(new RegisterSite(_nodeOptions.SiteId!, localSiteCommPath));
-
             _logger.LogInformation(
-                "Registered with Central at {CentralPath} as site {SiteId}",
+                "Configured central heartbeat path at {CentralPath} for site {SiteId}",
                 _communicationOptions.CentralActorPath, _nodeOptions.SiteId);
         }
     }

src/ScadaLink.Host/Components/App.razor

@@ -83,11 +83,14 @@
     <script src="/_framework/blazor.web.js"></script>
     <script>
         // Reconnection overlay for failover behavior
-        if (Blazor) {
-            Blazor.addEventListener('enhancedload', () => {
-                document.getElementById('reconnect-modal').style.display = 'none';
-            });
-        }
+        // Blazor object is available after blazor.web.js initializes
+        document.addEventListener('DOMContentLoaded', () => {
+            if (typeof Blazor !== 'undefined') {
+                Blazor.addEventListener('enhancedload', () => {
+                    document.getElementById('reconnect-modal').style.display = 'none';
+                });
+            }
+        });
     </script>
     <script src="/lib/bootstrap/js/bootstrap.bundle.min.js"></script>
 </body>

src/ScadaLink.Host/Program.cs

@@ -130,6 +130,7 @@ try
             ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
         });
 
+        app.MapStaticAssets();
         app.MapCentralUI<ScadaLink.Host.Components.App>();
         app.MapInboundAPI();
         await app.RunAsync();