feat: Render notifications in NotificationsView
This commit introduces the rendering of notifications within the Notifications tab. Instead of showing raw data, `NotificationsView` now uses `SkeetView` to display different notification types like follows, likes, reposts, replies, and quotes.
Specific changes include:
* A sealed `Notification` class was created to model different notification types.
* The `TimelineViewModel` now processes raw notification data from the API into this new `Notification` model. This involves fetching related records (like the post that was liked) to provide context.
* Added `fetchRecord` and `fetchActor` methods to the Bluesky data layer to retrieve individual posts and user profiles.
* `SkeetView` can now be tapped to handle replies from within the notifications list.