daemon: update monitor: implements ping/pong (required server changes)

kordophoned/src/daemon/signals.rs

@@ -18,4 +18,7 @@ pub enum Signal {
     /// - upload_guid: The GUID of the upload.
     /// - attachment_guid: The GUID of the attachment on the server.
     AttachmentUploaded(String, String),
+
+    /// Emitted when the update stream is reconnected after a timeout or configuration change.
+    UpdateStreamReconnected,
 }