Dashboard: admin-only Close session / Kill worker

Add IDashboardSessionAdminService (Admin-role gate, friendly errors,
audit logging) wrapping a new ISessionManager.KillWorkerAsync that
skips graceful shutdown and cleans up registry/metrics. Sessions,
Workers, and SessionDetails pages render Close / Kill buttons only
when CanManage; the service re-checks the role on every call so
forged clicks return Unauthenticated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.MxGateway.Server/Sessions/ISessionManager.cs

@@ -49,6 +49,19 @@ public interface ISessionManager
         string sessionId,
         CancellationToken cancellationToken);
 
+    /// <summary>
+    /// Forcefully terminates a session's worker without attempting graceful shutdown,
+    /// transitions the session to Closed, and removes it from the registry.
+    /// </summary>
+    /// <param name="sessionId">Identifier of the session whose worker to kill.</param>
+    /// <param name="reason">Reason for killing the worker (recorded in logs/audit).</param>
+    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
+    /// <returns>The result of closing the session.</returns>
+    Task<SessionCloseResult> KillWorkerAsync(
+        string sessionId,
+        string reason,
+        CancellationToken cancellationToken);
+
     /// <summary>Closes all sessions with expired leases at the specified time.</summary>
     /// <param name="now">The current time to evaluate expiration against.</param>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>