assistant2: Push logic for adding directory context down into the `ContextStore` (#22852)

This PR takes the logic for adding file context out of the
`DirectoryContextPicker` and pushes it down into the `ContextStore`.

Release Notes:

- N/A
69dde8e31dMarshall Bowers committed on 1/8/2025, 6:43:44 PM· committed by GitHubparent86f5bb1
2 files changedLine totals unavailable