This PR adds two new tools to Assistant 2:
- `list-worktrees` - Lists the worktrees in a project
- `read-file` - Reads a file at the given path in the project
I don't see `list-worktrees` sticking around long-term, as when we have
tools for listing files those will include the worktree IDs along with
the path, but making this tool available allows the model to utilize
`read-file` when it otherwise wouldn't be able to.
Release Notes:
- N/A
