- Add replay_dead_letter(conn, row_id): re-enqueues dead-lettered rows
  for retry by resetting attempt_count to 0 and status to 'pending'
- Add list_dead_letters(conn, limit): returns dead-lettered rows for
  operator review with event_key, source_table, last_error, timestamps
- CLI: --replay-dead-letter ROW_ID and --list-dead-letter commands
- Follows event bus dead-letter pattern for consistency