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.Commons/Messages/Management/ManagementCommandRegistry.cs

@@ -0,0 +1,36 @@
+using System.Collections.Frozen;
+
+namespace ScadaLink.Commons.Messages.Management;
+
+public static class ManagementCommandRegistry
+{
+    private static readonly FrozenDictionary<string, Type> Commands = BuildRegistry();
+
+    public static Type? Resolve(string commandName)
+    {
+        return Commands.GetValueOrDefault(commandName);
+    }
+
+    public static string GetCommandName(Type commandType)
+    {
+        var name = commandType.Name;
+        return name.EndsWith("Command", StringComparison.Ordinal)
+            ? name[..^"Command".Length]
+            : name;
+    }
+
+    private static FrozenDictionary<string, Type> BuildRegistry()
+    {
+        var ns = typeof(ManagementEnvelope).Namespace!;
+        var assembly = typeof(ManagementEnvelope).Assembly;
+
+        return assembly.GetTypes()
+            .Where(t => t.Namespace == ns
+                && t.Name.EndsWith("Command", StringComparison.Ordinal)
+                && !t.IsAbstract)
+            .ToFrozenDictionary(
+                t => t.Name[..^"Command".Length],
+                t => t,
+                StringComparer.OrdinalIgnoreCase);
+    }
+}