## Summary
- Remove the unused `ChatActivity.tsx` component
- Clean up all references including i18n translations (en, pt-BR, zh-CN)
- Update e2e test helpers and concurrent chat spec to remove
ChatActivity-related code

## Test plan
- [x] Lint checks pass
- [x] TypeScript compilation succeeds
- [x] All 33 test files pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)
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<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Removed the unused ChatActivity component and the bell entry point.
Updated tests and i18n; e2e now targets the chat tabs “in progress”
indicator instead of the activity list.

- **Refactors**
- Deleted ChatActivity.tsx and removed ChatActivityButton from TitleBar
and ActionHeader.
  - Removed related i18n keys in en, pt-BR, and zh-CN.
- Dropped e2e helpers for the activity list and updated
concurrent_chat.spec to select the “Chat in progress” tab.

<sup>Written for commit b005943bc7b87c8dfe6375504fbbbca088b7aabb.
Summary will update on new commits.</sup>

<!-- End of auto-generated description by cubic. -->

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Co-authored-by: Will Chen <willchen90@gmail.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>