Bug: `run-demo-mount-sources` test is broken

The issue:

```bash
2025-10-22T12:19:03.6700645Z > diracx-web-root@0.1.0-a10 prepare
2025-10-22T12:19:03.6700868Z > husky
2025-10-22T12:19:03.6700956Z
2025-10-22T12:19:03.6701034Z git command not found
2025-10-22T12:19:03.6701452Z added 1703 packages, and audited 1707 packages in 1m
2025-10-22T12:19:03.6701662Z
2025-10-22T12:19:03.6701747Z 398 packages are looking for funding
2025-10-22T12:19:03.6701986Z run `npm fund` for details
2025-10-22T12:19:03.6702127Z
...
2025-10-22T12:19:03.7352650Z > diracx-web-root@0.1.0-a10 dev
2025-10-22T12:19:03.7353206Z > npm --prefix packages/diracx-web run dev
2025-10-22T12:19:03.7353850Z
2025-10-22T12:19:03.7353898Z
2025-10-22T12:19:03.7354052Z > diracx-web@0.1.0-a10 dev
2025-10-22T12:19:03.7354481Z > export NEXT_PUBLIC_DIRACX_URL=$DIRACX_URL; next dev
2025-10-22T12:19:03.7354803Z
2025-10-22T12:19:03.7355166Z ▲ Next.js 15.3.1
2025-10-22T12:19:03.7355536Z - Local: http://localhost:8080
2025-10-22T12:19:03.7355989Z - Network: http://10.244.0.15:8080
2025-10-22T12:19:03.7356269Z
2025-10-22T12:19:03.7356439Z ✓ Starting...
2025-10-22T12:19:03.7356750Z ✓ Ready in 1806ms
2025-10-22T12:19:03.7357075Z ○ Compiling / ...
2025-10-22T12:19:03.7357442Z ✓ Compiled / in 6.5s (4709 modules)
2025-10-22T12:19:03.7357984Z ⨯ [TypeError: localStorage.getItem is not a function] {
2025-10-22T12:19:03.7358422Z digest: '3542577326'
2025-10-22T12:19:03.7358743Z }
2025-10-22T12:19:03.7359111Z [TypeError: localStorage.getItem is not a function]
2025-10-22T12:19:03.7359924Z ⨯ [TypeError: localStorage.getItem is not a function] { page: '/' }
2025-10-22T12:19:03.7360698Z (node:46) Warning: `--localstorage-file` was provided without a valid path
2025-10-22T12:19:03.7361498Z (Use `node --trace-warnings ...` to show where the warning was created)
2025-10-22T12:19:03.7363097Z ⨯ [TypeError: localStorage.getItem is not a function] {
2025-10-22T12:19:03.7363916Z digest: '3542577326'
2025-10-22T12:19:03.7364225Z }
2025-10-22T12:19:03.7364576Z [TypeError: localStorage.getItem is not a function]
2025-10-22T12:19:03.7365344Z ⨯ [TypeError: localStorage.getItem is not a function] { page: '/' }
2025-10-22T12:19:03.7365977Z ○ Compiling /_error ...
2025-10-22T12:19:03.7366304Z GET / 500 in 4994ms
```

The problem comes from `nodeImage` in `values.yaml` file, which points to the latest current node version. On October 15th, `v24` was replaced by `v25`.

```yaml
nodeImage: node:alpine
```

Using the `node:24-alpine` solves the immediate issue (https://github.com/DIRACGrid/diracx-charts/pull/189) but:
- we want to investigate why it does not work with `node:25-alpine`: probably because of WebStorage enabled by default (one could try disabling it with the `--no-webstorage` flag, I still don't know if it's the right approach).
- ideally, we would like to have a fixed version in `nodeImage`, that would be updated with `dependabot`/`renovate`.
- also ideally, it would be probably best to keep this node version in sync with the one we use in the `diracx-web` (and extension) dockerfile: https://github.com/DIRACGrid/diracx-web/blob/5b6b1b2fad260094d2848042a85dd0dc4257d0e3/Dockerfile#L5