d2b50e6cdc
- Add closed_at field to Issue type with JSON marshaling - Implement closed_at timestamp in SQLite storage layer - Update import/export to handle closed_at field - Add comprehensive tests for closed_at functionality - Maintain backward compatibility with existing databases Amp-Thread-ID: https://ampcode.com/threads/T-f3a7799b-f91e-4432-a690-aae0aed364b3 Co-authored-by: Amp <amp@ampcode.com>