Expand lint, CI, and dependency quality gates

[wilsonfreitas]

Summary

• add scheduled/manual integration and dependency-audit workflows
• freeze uv sync in existing CI workflows
• raise coverage fail-under to 80 and expand Ruff rules incrementally with B904, B905, and RUF100
• remediate vulnerable locked dependencies so the all-groups pip-audit check is clean

Verification

• uv run pytest -m "not integration": 185 passed, 11 deselected
• uv run ruff check bcb/ tests/
• uv run ruff format --check bcb/ tests/
• uv run mypy bcb/
• uv run --group docs sphinx-build -b html docs docs/_build/html
• uv run pytest --cov=bcb --cov-report=term-missing -m "not integration": 86.88 percent coverage, 80 percent required
• uv export --frozen --format requirements-txt --all-groups --no-emit-project --no-hashes -o /tmp/python-bcb-requirements-audit.txt
• uvx pip-audit --requirement /tmp/python-bcb-requirements-audit.txt: No known vulnerabilities found

Closes #41