build(deps): bump pinia from 2.3.0 to 2.3.1 in /frontend

Bumps [pinia](https://github.com/vuejs/pinia) from 2.3.0 to 2.3.1.
- [Release notes](https://github.com/vuejs/pinia/releases)
- [Commits](vuejs/pinia@v2.3.0...v2.3.1)

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

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

frontend/package.json

@@ -18,7 +18,7 @@
     "axios": "^1.7.8",
     "luxon": "^3.4.4",
     "oidc-client-ts": "^3.1.0",
-    "pinia": "^2.2.6",
+    "pinia": "^2.3.1",
     "pinia-plugin-persistedstate": "^4.2.0",
     "swiper": "^11.2.1",
     "vite": "^6.0.10",