After building roster-agent rows (unchanged), enumerate live sessions on
the mosaic-factory socket via `tmux list-sessions -F '#{session_name}'`.
Sessions not in the roster and not the holder session (_holder) are
emitted as additional UNMANAGED rows with runtime=unknown, managed=false,
source="socket". All existing roster rows gain managed=true/source="roster".
Roster rows always appear first; unmanaged rows follow.
- Adds buildTmuxListSessionsCommand + parseTmuxListSessions helpers
- driftFlag is always false for unmanaged rows (no roster runtime to compare)
- Heartbeat, pane, and systemd info populated for unmanaged rows the same
way as roster rows; tenant_id + host always present
- Resilient: if list-sessions fails, only roster rows are shown, no crash
- UNMANAGED flag appears in table output; managed/source fields in --json
- 8 new tests cover: command construction, session parsing, unmanaged row
inclusion, _holder exclusion, table flag, socket failure resilience
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RMoEx7hfdFGjUiCHuN1RRi
