Output GitHub Action results as a PR Comment

Currently, when `lockcheck` runs via the provided `action.yml` in a GitHub Actions workflow, it fails the build (Exit Code 1) and prints an error in the CI logs if critical vulnerabilities exist.

This is good, but for better Developer Experience (DX), the Action should be able to automatically post a comment on the Pull Request showing the Markdown-formatted table of the lockcheck findings.

**Acceptance Criteria:**
-
- Add an option to the `action.yml` (e.g., `post-pr-comment: true`).
- Write a lightweight node script or bash step inside the composite action that uses the `GITHUB_TOKEN` to hit the GitHub API.
- Post the parsed JSON findings as a formatted markdown comment on the active PR.

Start with action.yml and trace how lockcheck findings are produced and exposed to the action. Review the GitHub Actions context and GITHUB_TOKEN API flow needed for the active pull request. Done means an opt-in setting posts the parsed findings as a Markdown comment while preserving the existing failure behavior for critical vulnerabilities.

Written by the indexing model from the issue text.