Add import filter controls

[solomonneas]

Summary

• add metadata filters to work import list, triage, promote, and dismiss
• add filtered bulk dismissal with work import dismiss --all
• add handoff issue category filters to handoff issues and handoff import-issues
• document batch promotion/dismissal examples for scanner-specific metadata

Verification

• .venv/bin/python -m pytest tests/test_work_cmd.py tests/test_handoff_cmd.py -q
• .venv/bin/python -m pytest -q
• git diff --check
• content-guard public scan
• brigade handoff issues --target . --category route-skip --limit 5
• brigade handoff import-issues --target . --category route-skip --dry-run
• brigade work import list --target . --source handoff-ingest --metadata handoff_issue_category=skip --limit 2
• brigade work import triage --target . --source handoff-ingest --metadata handoff_issue_category=route-skip --limit 3
• dogfooded filtered promote and dismiss against local handoff-ingest imports