fix: add collapse all threads functionality to email selection in thr…

[maxhaomh]

Summary

When interacting with threads in the email lists, they will automatically close when you switch to another thread. This behavior is adjacent to Microsoft Outlook. Enhances UI to ensure uniform alignment between threaded and standard conversations.

Changes

• collapseAllThreads added to email-list.tsx — when selecting an email outside an expanded thread, all other threads collapse first
• onCollapseAllThreads prop threaded through thread-list-item.tsx — called before expanding a new thread to ensure only one thread is open at a time
• Expand-toggle button moved from below the thread row to a badge overlaid on the avatar (bottom-center), restyled with a smaller 3h icon and circular background/border

Related Issues

Closes #

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactor / code quality improvement
• Chore / dependency update / CI change

Checklist

• I have read the Contributing Guide
• My code follows the project's code style and conventions
• I have run npm run typecheck && npm run lint and there are no errors
• The build passes (npm run build)
• I have tested my changes locally
• I have added or updated documentation if needed
• I have updated translations (locales/) if my changes affect user-facing text
• I have included screenshots or a screen recording for UI changes

Screenshots / Demo

Notes for Reviewers