Frontend: Invalidate ping query to update message badges

[nabramow]

Frontend pingQueryKey invalidation: makes the UI update immediately. Without it, the frontend won't refetch the ping query until its natural 10-second polling interval fires — so the bell badge would still show the old stale count for up to 10 seconds, even though the backend data is already correct.

Closes #8312

Testing

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Web frontend checklist

• There are no console warnings when running the app
• Added tests where relevant
• Clicked around my changes running locally and it works
• Checked Desktop, Mobile and Tablet screen sizes

For maintainers

• Maintainers can push commits to my branch
• Maintainers can merge this PR for me

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Project	Deployment	Actions	Updated (UTC)
couchers	Ready	Preview	May 23, 2026 8:44am

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📝 Release Notes

This PR should be included in the release notes.

Suggested release note:

Fixed message badges so read messages are marked as read immediately instead of appearing unread for several seconds

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: include
Reasoning: This fixes a noticeable user-facing bug where message/notification badges could continue showing unread items for up to 10 seconds after messages were read. It improves the accuracy and responsiveness of message status in the UI, which users would notice.