feat(vscode-webui): add unified background job and terminal manage panel

[liangfung]

Summary

• Consolidates background tasks and terminals into a single unified dropdown panel in the top-right of the chat view.
• Enhances visual consistency with stylized status dots and spinners, and supports collapsible lists for dense background task histories.
• Refines terminal state tracking with custom isRunning and lastCommand properties.

Screenshot

Test plan

• Run package unit tests in packages/vscode-webui (bun run test) to verify manage-panel.test.tsx, background-task-debug-panel.test.tsx, and build-job-list.test.ts.
• Verify compilation and linting by running bun check and bun tsc.

🤖 Generated with Pochi | Task

[codecov-commenter]

Codecov Report

❌ Patch coverage is 70.99698% with 192 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.49%. Comparing base (1dd2300) to head (f386bf7).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...at/components/__stories__/manage-panel.stories.tsx	1.05%	94 Missing ⚠️
packages/vscode-webui/src/components/ui/sheet.tsx	25.00%	81 Missing ⚠️
...ebui/src/features/chat/components/manage-panel.tsx	97.00%	8 Missing ⚠️
...code-webui/src/features/chat/hooks/use-job-list.ts	50.00%	6 Missing ⚠️
...es/chat/components/background-task-debug-panel.tsx	95.74%	2 Missing ⚠️
...scode-webui/src/lib/background-job-status-label.ts	92.30%	1 Missing ⚠️

❌ Your patch status has failed because the patch coverage (70.99%) 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    #1926      +/-   ##
==========================================
+ Coverage   33.31%   33.49%   +0.17%     
==========================================
  Files         778      785       +7     
  Lines       83119    83600     +481     
  Branches     4734     4947     +213     
==========================================
+ Hits        27695    28003     +308     
- Misses      55304    55477     +173     
  Partials      120      120              

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