⬆️ Bump knip from 2.25.2 to 2.28.0 in /frontend

Bumps [knip](https://github.com/webpro/knip) from 2.25.2 to 2.28.0.
- [Release notes](https://github.com/webpro/knip/releases)
- [Changelog](https://github.com/webpro/knip/blob/main/docs/release-notes-v2.md)
- [Commits](webpro-nl/knip@2.25.2...2.28.0)

---
updated-dependencies:
- dependency-name: knip
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

frontend/package.json

@@ -41,7 +41,7 @@
     "elm-review": "^2.10.2",
     "elm-test": "^0.19.1-revision12",
     "firebase-tools": "^12.5.4",
-    "knip": "^2.25.2",
+    "knip": "^2.28.0",
     "prettier": "^3.0.3",
     "rimraf": "^5.0.1",
     "size-limit": "^9.0.0",