MISSING FROM BUZZ: working set, labelled work items (not just channels/threads as bags of words)

**Motivation**
When working on tasks, they end up in channels and reply threads with little find-ability, and no quick way to jump channels and threads. You end up having to find the thread by words (most threads start with @-mentions so you have to jump past that to try and figure out what the thread is about), and you lose context and position with every jump.

We need a way to relabel a thread as a work item, and that adds it to your working set list that can be quickly hopped between without losing your scroll position within the item, your unread items, etc. A 0-lag hop. Bounce between your convos.

NO, INBOX IS NOT THIS, it is just "@yourownname bla bla bla" repeated 1000 times and doesn't help to jump where you want to check on updates.

Try having 3 continuous conversations in 3 channels with bots and hop between them and keep them all moving at same time and suffer, then you will understand this request. Suffering drives innovation?

**Proposed solution**
Some gesture to relabel a thread as a "work item" within your personal "working set", add it with a title and it goes into a list of those that you can archive and manage with quick hops between your in flight tasks. These are pointers into the channel/threads that retain your scroll, and visual state and are fast hops without having to re-find where you were prior.

**Alternatives considered**
Other forms of self harm via UX, but decided one was enough.

**Additional context**
Use Buzz for real work, something like this should be the thing nagging your every awake minute.

No files, tests, or entry points are named. Start by locating the existing channel/thread navigation and inbox behavior, then determine how a personal working set could fit alongside them. Done should include relabeling threads, quick navigation, preserved scroll and unread state, and archiving.

Written by the indexing model from the issue text.