Fix notification message for posts with no text content (#31007)

* Fix notification message for posts with no text

Changed the default notification message from "did something new" to
"posted a message" for better clarity when receiving notifications
from posts with no readable text content.

Fixes: MM-61948

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* address feedback from code review

---------

Co-authored-by: Claude <noreply@anthropic.com>

e2e-tests/cypress/tests/integration/channels/notifications/desktop_notifications_1_spec.js

@@ -144,7 +144,7 @@ describe('Desktop notifications', () => {
         spyNotificationAs('withNotification', 'granted');
 
         const actualMsg = '---';
-        const expected = '@' + otherUser.username + ' did something new';
+        const expected = '@' + otherUser.username + ' posted a message';
 
         // # Ensure notifications are set up to fire a desktop notification for all activity.
         changeDesktopNotificationAs('all');