Mark as unread

### Your use case

#### What would you like to do?

I would like to mark a chat as unread, which should also show a badge icon on the app icon on the Homescreen

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

Because I often read a message and can't give an answer right away, closing the app without responding and forget about it.

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

I just need an Options anywhere in the overview of all chats to mark a specific chat as unread

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

The issue names the chat overview and the app icon badge but no files or tests. Start by locating the chat overview's options and the existing unread and badge behavior; done means a specific chat can be marked unread and the app icon shows the corresponding badge.

Written by the indexing model from the issue text.