ci: vendor validation scripts and remove remote action pins

[hyperpolymath]

Automated PR to fix CI after deleted actions.

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Summary by Gitar

• CI / Workflows:
  • Vendored A2ML and K9 validation scripts into .githooks/
  • Replaced remote action pins with local script execution in dogfood-gate.yml

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[gitar-bot]

Code Review ✅ Approved

Vendors A2ML and K9 validation scripts into .githooks/ and updates dogfood-gate.yml to execute them locally instead of using remote action pins. No issues found.

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