BUG: Users can reply to archived threads

Editing and replying functionality is still allowed on archived posts. It shouldn't be.

**Example**
https://www.metastaging.net/2503/does-rich-text-editing-work

<img width="853" height="128" alt="Image" src="https://github.com/user-attachments/assets/feb1ae19-1419-4465-a320-18d63b487557" />