docs: add git watcher script task + update engineer_states schema
- PLAN.md: add task 2b — scripts/podman-agent.mjs writes git signals
directly to MongoDB (changedFiles, diffStat, branch, recentCommit)
every 15s; Hermes reads merged vision+git state for event detection
- mongodb.md: extend engineer_states with git fields, document two-writer
upsert pattern (vision fields vs git fields, no conflict)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FFbfi4Cmb7BY75Wtne7bZn
