Sentinel 0.2.1

Fixes

• CI security job passes again — bandit's B608 suppression directives were on the wrong lines in sentinel/db.py, failing the security gate on main. The # nosec comments now sit on the exact lines bandit flags, and explanatory text was moved off the directive lines. bandit -q -r sentinel exits 0 with no findings.

No functional changes — 0.2.0 features (PyPI/npm monitors, sentinel uptime, retention_days) are unchanged.