chore: bump postcss from 8.4.38 to 8.4.39 in /frontend/web (#213)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.38 to 8.4.39.
- [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/8.4.38...8.4.39)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

frontend/web/package.json

@@ -45,7 +45,7 @@
     "eslint-plugin-prettier": "^5.1.3",
     "eslint-plugin-react": "^7.34.3",
     "long": "^5.2.3",
-    "postcss": "^8.4.38",
+    "postcss": "^8.4.39",
     "prettier": "^3.3.2",
     "protobufjs": "^7.3.2",
     "typescript": "^5.5.2",