fix(frontend): タブがアクティブな間はstreamが切断されないように

Fix #10952

packages/frontend/src/stream.ts

@@ -12,5 +12,14 @@ export function useStream(): Misskey.Stream {
 		token: $i.token,
 	} : null));
 
+	window.setTimeout(heartbeat, 1000 * 60);
+
 	return stream;
 }
+
+function heartbeat(): void {
+	if (stream != null && document.visibilityState === 'visible') {
+		stream.send('ping');
+	}
+	window.setTimeout(heartbeat, 1000 * 60);
+}