Keyboard shortcut for "mark room as read"

### Your use case

It seems like it will still be some time until the unread notifications bugs are all fixed. In the meantime, it would be very useful to have a keystroke option to "mark all as read" in current room to be able to more quickly dismiss the unread status for rooms sequentially. It's somewhat laborious to have to right click on each room separately and pick this option.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

The issue names no files, tests, or entry points. Start by locating the existing “mark all as read” room action and the application’s keyboard-shortcut handling, then verify the shortcut works for the current room and does not conflict with existing bindings.

Written by the indexing model from the issue text.