[FEATURE] Add keyboard shortcut to expand/collapse completed subtasks in the task list

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When Claude Code's task list contains completed subtasks, they are collapsed into a single line like ... +3 completed. Currently, the only way
to expand this and see the completed items is by clicking with the mouse. For users who prefer keyboard-driven workflows (e.g., using Ctrl+T
to toggle the task panel), this forces an awkward switch to the mouse just to review what was done. This breaks flow and slows down
keyboard-centric usage.

Proposed Solution

Add a keyboard shortcut — either Enter or Space when a task row is focused — to toggle the expand/collapse state of the ... +N completed
group. An alternative would be a dedicated global binding like Ctrl+E that expands/collapses the completed group under the currently selected
task. The behavior should mirror what clicking does today: show/hide the list of completed subtasks inline.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

1. Claude Code is working through a multi-step task with 5+ subtasks
2. The task list shows ... +4 completed under the parent task
3. The user presses Ctrl+T to focus the task panel, navigates to the task row with arrow keys, and presses Enter
4. The 4 completed subtasks expand inline, showing what was done — all without touching the mouse
5. Pressing Enter again collapses them back to ... +4 completed

Additional Context

_No response_