[FEATURE/CI] Architect Native GitLab CI Pipeline Template and Variable Mapping

[squid-protocol]

Objective: Translate the GitHub Action execution context into a native GitLab CI template.
Tasks:

• Map ${{ secrets.GITHUB_TOKEN }} equivalent to $CI_JOB_TOKEN.
• Map ${{ github.workspace }} equivalent to $CI_PROJECT_DIR.
• Ensure the Docker image execution routes standard JSON payloads and SARIF uploads correctly into GitLab's native vulnerability UI.
• Publish as templates/gitlab-ci-template.yml.