Fix vulnerable lint dependencies

[bvolpato]

Summary

The lint tooling dependency tree contains vulnerable versions of brace-expansion and KaTeX. Update both so a clean install has no npm audit findings.

Changes

• Update the locked brace-expansion dependency from 5.0.9 to 5.0.12.
• Override KaTeX under micromark-extension-math to 0.18.2, which fixes GHSA-238p-pmpm-9mq7. The extension's declared ^0.16.0 range excludes the security fix.
• Update the corresponding registry URLs and integrity checksums.

Testing

Validated locally with Node.js 22.22.2 and npm 10.9.7:

• npm ci --ignore-scripts: clean install succeeds.
• npm run lint:all: passes.
• npm audit --audit-level=low: zero vulnerabilities.
• npm ls katex micromark-extension-math brace-expansion: confirms the patched versions and scoped override.
• Smoke checks pass for ESLint Markdown parsing with math enabled, micromark inline/display math rendering, and invalid-command handling with errors enabled and disabled.
• git diff --check: passes.