fix: replace default CodeQL setup with Actions-only scan

[stuckvgn]

Summary

• CodeQL default setup was auto-configured to scan javascript-typescript, but this repo contains only markdown and YAML configuration files -- no JS/TS source code
• Error: CodeQL detected code written in GitHub Actions, but not any written in JavaScript/TypeScript
• Disabled the broken default setup via API and added an explicit workflow that scans only the actions language (GitHub Actions YAML files)

What changed

• Disabled CodeQL default setup (was misconfigured for javascript-typescript)
• Added .github/workflows/codeql.yml configured to scan only actions language
• Runs on push/PR to main and weekly schedule

Test plan

• Verify the new CodeQL workflow passes on merge to main
• Confirm no more "configuration error" status on the repo's code scanning page

[github-advanced-security]

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