feat: add HTTP Management API, migrate CLI from Akka ClusterClient to HTTP

Replace the CLI's Akka.NET ClusterClient transport with a simple HTTP client
targeting a new POST /management endpoint on the Central Host. The endpoint
handles Basic Auth, LDAP authentication, role resolution, and ManagementActor
dispatch in a single round-trip — eliminating the CLI's Akka, LDAP, and
Security dependencies.

Also fixes DCL ReSubscribeAll losing subscriptions on repeated reconnect by
deriving the tag list from _subscriptionsByInstance instead of _subscriptionIds.

src/ScadaLink.Host/Actors/AkkaHostedService.cs

@@ -192,6 +192,8 @@ akka {{
             Props.Create(() => new ScadaLink.ManagementService.ManagementActor(_serviceProvider, mgmtLogger)),
             "management");
         ClusterClientReceptionist.Get(_actorSystem).RegisterService(mgmtActor);
+        var mgmtHolder = _serviceProvider.GetRequiredService<ScadaLink.ManagementService.ManagementActorHolder>();
+        mgmtHolder.ActorRef = mgmtActor;
         _logger.LogInformation("ManagementActor registered with ClusterClientReceptionist");
 
         _logger.LogInformation("Central actors registered. CentralCommunicationActor created.");