[Notifications] Add a Mentions tab (#7044)

* Split out NotificationsTab

* Remove unused route parameter

* Refine the split between components

* Hoist some logic out of NotificationFeed

* Remove unused option

* Add all|conversations to query, hardcode "all"

* Add a Conversations tab

* Rename to Mentions

* Bump packages

* Rename fields

* Fix oopsie

* Simplify header

* Track active tab

* Fix types

* Separate logic for tabs

* Better border for first unread

* Highlight unread for all only

* Fix spinner races

* Fix fetchPage races

* Fix bottom bar border being obscured by glimmer

* Remember last tab within the session

* One tab at a time

* Fix TS

* Handle all RQKEY usages

* Nit

src/view/screens/DebugMod.tsx

@@ -872,7 +872,13 @@ function MockNotifItem({
       </P>
     )
   }
-  return <NotificationFeedItem item={notif} moderationOpts={moderationOpts} />
+  return (
+    <NotificationFeedItem
+      item={notif}
+      moderationOpts={moderationOpts}
+      highlightUnread
+    />
+  )
 }
 
 function MockAccountCard({