[FeatureRequest] Archive rooms

### Your use case

#### What would you like to do?

Archive rooms like in WhatsApps

#### Why would you like to do it?

I can't have a clean space with my conversations because I always have some conversation that I need to archive.
I would reuse them later but right now they are just taking rooms for nothing.

#### How would you like to achieve it?

- auto-unarchive when receiving a message in the room
- new section with the archived rooms

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

Begin with the use case and requested behavior in issue #1402. Determine which Element client owns room-list state and navigation, then define the scope for archived-room display and automatic unarchiving when messages arrive. No files, tests, or entry points are named, so implementation locations and validation steps still need to be identified.

Written by the indexing model from the issue text.