fix: Fix single-select checkbox state in planning mode

[charlesvien]

Problem

In single-select mode, clicking the "Other" option enters edit mode without clearing the previous selection, and typing auto-checks "Other" without clearing others so you end up with two items checked. Then you can't uncheck either because single-select toggleCheck always re-selects the clicked item.

Changes

1. Allow unchecking a selected option in single-select mode (toggleCheck)
2. Clear other selections when clicking a custom-input option in single-select mode (handleClick, selectCurrent)
3. Clear other selections when auto-checking custom input on text entry in single-select mode (handleCustomInputChange)

How did you test this?

Manually

[charlesvien]

• fix: Keep prompt visible during task creation #1314
• feat: Add initial task mode setting #1313
• fix: Fix single-select checkbox state in planning mode #1312 👈 (View in Graphite)
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.