Automatically remove read items under the Unread tab

[byfnoel]

This change ensures that when an item is selected to read under the Unread tab, it is automatically removed from view.

I'd also like to note that the item remains accessible in inbox and in the author's individual feed.

[byfnoel]

This is a stopgap to the long-term desire behavior explain in issue 8. This issue is proven to be somewhat complicated after working on different approaches locally.

@parksb I'd love to get this reviewed and hopefully get merge.

[parksb]

The behavior where items don't immediately disappear from the list when read in the Unread tab is intentional.

If items were to disappear from the list immediately upon being read, as implemented in this PR, there would be three issues: (1) Having an item disappear the moment you click on it is unexpected behavior. The UI flickering shown in the video is particularly not ideal. (2) The user ends up seeing the list where nothing is selected, but the item's content is still displayed on the side. (3) Once an item disappears from the list, there's no way to Mark as unread or Save it.

Screen.Recording.2026-01-21.at.20.11.30.mov

I think the best way to resolve #8 would be to introduce a new feature like 'Archive' and 'Mark this page as archived'.