Add GitLab CI template and SAST report conversion for scanner

[yashiagar2507]

Closes #5.

Adds a GitLab CI integration for ISNAD Scanner:

• Adds a reusable GitLab CI template under scanner/examples/gitlab
• Adds a converter from ISNAD batch JSON to GitLab SAST JSON
• Documents scan target/report/failure-mode configuration
• Links the GitLab CI guide from scanner and docs READMEs
• Fixes batch --json output so machine-readable output is not polluted by progress logs

Verified:

• npm ci
• npm run build
• npm --silent run scan -- batch "/private/tmp/isnad-sample.js" --json
• node scripts/isnad-to-gitlab-sast.mjs /private/tmp/isnad-scan-results.json /private/tmp/gl-sast-isnad.json

[vercel]

@yashiagar2507 is attempting to deploy a commit to the Rapi's projects Team on Vercel.

A member of the Team first needs to authorize it.

[yashiagar2507]

Note: the Vercel check is blocked on fork deployment authorization. Local verification passed with npm ci, npm run build, and a scanner-to-GitLab-SAST conversion smoke test.

[yashiagar2507]

Hi! Just checking whether this matches the expected direction for #5. Happy to adjust the GitLab report format, template location, or CI job shape if you prefer a different integration style.