Replace the comment-only list with a Linear-style unified timeline that
interleaves field changes and comments chronologically.
Backend:
- activity_listeners.go: records field changes (status, assignee, description,
task completed/failed) to activity_log table on domain events
- Timeline API: GET /api/issues/{id}/timeline merges activity_log + comments
sorted by created_at
- Comment reply: parent_id column + handler support for threading
Frontend:
- Unified timeline replaces comment list: activity entries as compact muted
lines, comments as Card components with reply threading
- Filter toggle (All / Comments / Activity)
- Reply UI: inline editor under comments with Cancel/Reply buttons
- Real-time sync for activity:created + comment events
- 10 new Go tests, all passing
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
e7fe6ea79b