Three fixes for the coordinator pipeline:
1. Use bandit.yaml config file (-c bandit.yaml) so global skips
and exclude_dirs are respected in CI.
2. Upgrade pip to >=25.3 in the install step so pip-audit doesn't
fail on the stale pip 24.0 bundled with python:3.11-slim.
3. Clean up nosec inline comments to bare "# nosec BXXX" format,
moving explanations to a separate comment line above. This
prevents bandit from misinterpreting trailing text as test IDs.
Fixes#365
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>