fix(vscode-webui): display subagent todo list regardless of toggle status

[wsxiaoys]

Summary

• Render the subagent's todo list using a separate TaskThread as the detail prop of ExpandableToolContainer.
• Position {detail} above {showDetails && expandableDetail} in ExpandableToolContainer to ensure that when expanded, the todo list is rendered immediately below the header block (and above the list of steps), matching the design specification.
• Set showTodos={false} in the main expandable detail's TaskThread to prevent duplicate todo list rendering when expanded.
• Added and updated storybooks (new-task-tool-gallery.stories.tsx and subtask-agent.stories.tsx) to showcase and verify this behavior.

Screenshots

Correct Behavior (Both Collapsed & Expanded)

• Collapsed: The todo list is displayed immediately below the header.
• Expanded: The todo list is displayed immediately below the header, and the list of steps is displayed below it.

Test plan

• Open the Storybook and navigate to the SubtaskAgent or NewTask components.
• Verify that the todo list is displayed for collapsed subagent tool calls.
• Verify that expanding the subagent details renders the list of steps below the todo list, and does not duplicate the todo list.

🤖 Generated with Pochi | Task

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 23.77%. Comparing base (34565b6) to head (a1ca4ad).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
...ools/__stories__/new-task-tool-gallery.stories.tsx	0.00%	35 Missing ⚠️
...atures/tools/__stories__/subtask-agent.stories.tsx	0.00%	13 Missing ⚠️
...i/src/features/tools/components/new-task/index.tsx	0.00%	12 Missing ⚠️
...i/src/features/tools/components/tool-container.tsx	0.00%	1 Missing ⚠️

❌ Your patch status has failed because the patch coverage (0.00%) is below the target coverage (75.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1602      +/-   ##
==========================================
+ Coverage   22.31%   23.77%   +1.45%     
==========================================
  Files         737      742       +5     
  Lines       72789    74555    +1766     
  Branches     1913     2127     +214     
==========================================
+ Hits        16244    17723    +1479     
- Misses      56254    56550     +296     
+ Partials      291      282       -9     

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