This PR factors a new `ActiveThread` view out of the `AssistantPanel` to
group together the state that pertains solely to the active view.
There was a bunch of related state on the `AssistantPanel` pertaining to
the active thread that needed to be initialized/reset together and it
makes for a clearer narrative is this state is encapsulated in its own
view.
Release Notes:
- N/A
This PR adds the ability to open past threads in Assistant 2.
There are also some mocked threads in the history for testing purposes.
Release Notes:
- N/A
This PR adds support to Assistant 2 for using tools provided by context
servers.
As part of this I introduced a new `ThreadStore`.
Release Notes:
- N/A
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Co-authored-by: Cole <cole@zed.dev>
