feat(cli): add fail-on-findings option

[deepujain]

Summary

• add an opt-in --fail-on-findings gate for active findings below the aggregate risk threshold
• apply the gate to single and recursive scans after reports are written
• cover the low-risk single-scan and recursive cases

Validation

• ruff format --check src/skillspector/cli.py tests/unit/test_cli.py
• ruff check src/skillspector/cli.py tests/unit/test_cli.py
• git diff --check
• python3 -m py_compile src/skillspector/cli.py tests/unit/test_cli.py
• focused pytest could not collect locally because the temporary Python environment did not retain package metadata; CI is the remaining test surface

Fixes #448

Signed-off-by: Deepak Jain deepujain@gmail.com