security: add CodeQL analysis

[vitormattos]

Summary

Add CodeQL semantic analysis for the JavaScript/TypeScript governance engine.

• runs on pull requests, main, and a weekly schedule;
• uses only contents: read and security-events: write;
• pins CodeQL actions to the immutable commit for v4.38.1;
• does not make the check required yet.

After one successful baseline run, we can confirm the exact check context and then add it to the caller-managed governance ruleset. This advances #23.

[github-advanced-security]

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