fix: remove dead briefing.md creation, add pid to identity change log
- Remove empty sol/briefing.md creation from ensure_sol_directory() —
nothing writes to it (morning briefing outputs to YYYYMMDD/agents/)
- Add pid field to identity change records in sol/history.jsonl for
correlating changes with agent processes in cortex logs
From expert review panel findings #13 and #14.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>