build(deps): bump katex from 0.16.19 to 0.16.21

Bumps [katex](https://github.com/KaTeX/KaTeX) from 0.16.19 to 0.16.21.
- [Release notes](https://github.com/KaTeX/KaTeX/releases)
- [Changelog](https://github.com/KaTeX/KaTeX/blob/main/CHANGELOG.md)
- [Commits](KaTeX/KaTeX@v0.16.19...v0.16.21)

---
updated-dependencies:
- dependency-name: katex
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -30,7 +30,7 @@
     "clsx": "^2.1.1",
     "es-toolkit": "^1.31.0",
     "gray-matter": "^4.0.3",
-    "katex": "^0.16.19",
+    "katex": "^0.16.21",
     "next": "15.1.4",
     "react": "19.0.0",
     "react-dom": "19.0.0",