[feature]: Mark notifications read through the public API #10217

Is there an existing issue for this?

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Summary

The public API's notification endpoints only accept GET. Please add a way to mark one notification, or all of them, as read with an API key, the same thing the Inbox's mark-as-read does.

Why should this be worked on?

Most of our notifications need no action: target date, cycle and state changes on tickets we're only following. We filter those out automatically in an internal dashboard so the few that need us stand out. But the API can't mark the rest read, so every one still has to be cleared by hand in Plane. The app's own mark-read endpoint only accepts a browser login, so API-key integrations have no supported way to do it.