ci: adopt central Tutorial PR Checks, remove CircleCI

[sap-tutorials-builder]

Summary

This PR installs the central org-maintained PR content checks:

• Adds — runs markdownlint, link check, gitleaks on PRs (notify-only, never blocks merge)
• Adds — posts sticky PR comment via the SAP Tutorials GitHub App
• Removes all files under — CircleCI is replaced by the central GitHub Actions pipeline

Both callers delegate to at . Central non-breaking changes propagate with no per-repo edits.

Generated by the rollout workflow in .

[CLAassistant]

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