feat: add acceptance criteria to work tasks

[solomonneas]

Summary

• add task type, priority, and repeatable acceptance criteria to the local work task ledger
• add brigade work task plan and acceptance coverage in work brief
• pass accepted ledger criteria into the work run task prompt when consuming a queued task

Verification

• .venv/bin/python -m pytest 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
• CLI smoke: brigade work task add, brigade work task plan, and brigade work brief in a temporary repo