feat(tui): allow searching for tasks (#9042)
### Description
This PR adds the ability to search though the task list by using `/` and
scroll through the results with the arrow keys.
A user can exit the search by pressing `Esc` or `Backspace` when there
search bar is already empty to return the the selected task before the
search. If they press `Enter` it will exit the search at selected
result.
Searching is currently done via a naive substring search, but could be
enhanced with a fuzzy matcher if desired.
Each commit can be reviewed on it's own.
### Testing Instructions
Extensive unit tests for state changes.
https://github.com/user-attachments/assets/8cc06e76-e2c8-4639-9c2b-db0d8ae5c636
