ci: Add blocked keywords

[ivov]

Summary by cubic

Block security-related keywords in PR titles to prevent sensitive disclosures. CI now fails with a clear error asking authors to reword titles.

• New Features
  • Added validation to reject PR titles containing security terms (e.g., XSS, RCE, CVE, SSRF, injection).
  • Added unit tests and a specific error message: “PR title contains security-related keywords. Reword it and resubmit.”

^{Written for commit a8405e2. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files