feat: sync handoff ingest issues

[solomonneas]

Summary

• add brigade handoff sync-issues to import only new handoff-ingest issues
• close stale handoff-ingest imports and tasks when the latest scan no longer reports their issue id
• keep work brief focused on new handoff issues while counting known ones quietly

Root cause

handoff import-issues could import issue records, but there was no reconciliation step after the underlying latest log changed. Resolved route-skip imports and promoted tasks stayed pending in the daily work loop even after the route-skip root cause was fixed.

Validation

• .venv/bin/python -m pytest tests/test_handoff_cmd.py tests/test_work_cmd.py -q
• .venv/bin/python -m pytest -q
• git diff --check
• PYTHONPATH=$HOME/repos/content-guard/src .venv/bin/python -m content_guard scan . --policy $HOME/repos/content-guard/policies/public-repo.json
• .venv/bin/brigade handoff sync-issues --target .
• .venv/bin/brigade work brief --target .