feat: add daily work brief

[solomonneas]

Summary

• add brigade work brief and --json as a start-of-day daily work entrypoint
• make next-step extraction handle markdown ## Next sections and fallback to summary.md
• route dogfood status/next and work snapshots through the same run-level extraction path

Verification

• .venv/bin/python -m pytest tests/test_work_cmd.py tests/test_dogfood_cmd.py -q
• .venv/bin/brigade work brief --target . --limit 3
• .venv/bin/brigade work brief --target . --json
• .venv/bin/python -m pytest -q
• PYTHONPATH=/home/clawdbot/repos/content-guard/src python3 -m content_guard scan . --policy /home/clawdbot/repos/content-guard/policies/public-repo.json
• git diff --check