bug(playwright): sheets created by the playwright tests are never cleaned up

We should extend the playwright test called ''Delete multiple old pages' to also clean up .json documents (sheets) as they are currently never cleaned up.

This applies to both Helix 6 as well as the DA-Admin backends.

Start with the Playwright test named "Delete multiple old pages" and inspect how it currently removes old pages. Extend that test's cleanup to cover .json documents for both the Helix 6 and DA-Admin backends, then run the relevant Playwright test and confirm the sheets are removed.

Written by the indexing model from the issue text.