Add scripts/update_checker.py — dependency health monitor that checks
installed Python packages against PyPI latest, classifies updates by
semver (major/minor/patch), flags breaking changes, and outputs a
human-readable or JSON report.
Acceptance criteria:
✓ Compares installed vs latest via pip list + PyPI JSON API
✓ Reports major/minor/patch updates with severity (high/medium/low)
✓ Flags breaking changes (major version jumps)
✓ Output: formatted text report or --json machine report
Also adds comprehensive test suite (11 tests, all passing).
Refs: #109
