feat: settings redesign, rich text mentions, inbox listeners, and UI polish
- Refactor settings page into tabbed components (general, workspace, members, tokens, account)
- Move settings link from dropdown to sidebar nav
- Add @mention suggestions in rich text editor
- Expand inbox listeners with enhanced event handling
- Improve board column, issue detail, and create issue modal UX
- Update markdown rendering and code block styling
- Polish skills page layout
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>