chore(deps-dev): bump postcss from 8.5.6 to 8.5.12 in /frontend (#32)

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.6 to 8.5.12.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.5.6...8.5.12)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.12
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

frontend/package.json

@@ -42,7 +42,7 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.4.24",
     "globals": "^16.5.0",
-    "postcss": "^8.5.6",
+    "postcss": "^8.5.12",
     "tailwindcss": "^4.1.17",
     "typescript": "~5.9.3",
     "typescript-eslint": "^8.46.4",