fix(historian-gateway): dispose alarm-write channel at shutdown + ServerHistorian startup diagnostic

Claude-Session: https://claude.ai/code/session_012SDSQ3AcaXqPcBtDESBRii

src/Core/ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian/SqliteStoreAndForwardSink.cs

@@ -732,12 +732,13 @@ public sealed class SqliteStoreAndForwardSink : IAlarmHistorianSink, IDisposable
     /// <summary>Gets the current exponential backoff delay for retry operations.</summary>
     public TimeSpan CurrentBackoff => BackoffLadder[_backoffIndex];
 
-    /// <summary>Disposes the sink and releases all held resources including the drain timer.</summary>
+    /// <summary>Disposes the sink and releases all held resources including the drain timer and the writer.</summary>
     public void Dispose()
     {
         if (_disposed) return;
         _disposed = true;
         _drainTimer?.Dispose();
         _drainGate.Dispose();
+        if (_writer is IDisposable writerDisposable) writerDisposable.Dispose();
     }
 }