Add --min-severity flag to control which findings appear in reports

[Sasireddy001]

This PR closes #7.

It adds a --min-severity option to skillfrisk scan so you can filter findings down to a minimum severity:

• low (default) — show everything
• medium
• high
• critical

The filter applies to the terminal table, JSON, SARIF, and HTML outputs, and it also updates the exit code so the report and CI result stay consistent.

I added tests for the high and medium thresholds, invalid values, and the --no-fail-on-high interaction, and updated the README with an example.

[Sasireddy001]

Hi! Just a friendly follow-up.

The implementation, tests, and documentation updates are complete. It looks like the remaining step is workflow approval for external contributors so CI can run.

Thank you for taking a look.

[Topicspot]

Thanks for picking this up, and for reading the codebase first. The filter lands in the right place, before any rendering, so the table, JSON, SARIF, HTML, the risk score and the exit code all tell the same story, which is exactly what #7 asked for. Reusing the --fail-on validation pattern from diff keeps the CLI consistent. I ran the branch through the full local gate (ruff, mypy, pytest, vulture) and everything passes. Fork CI needs a manual approval this setup cannot give, so I verified locally instead. Merging.