Enhancement: default save Deck files to /Deck instead of /

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Is your feature request related to a problem? Please describe.
When you create a guest account, that has allowed access to Nextcloud Deck, when you log in, you see all of the files from Deck in / as the user doesn't have access to Deck settings via Nextcloud settings, where the folder path setting is located.

Describe the solution you'd like
Be able to else set the location from deck settings in app, ar default saving files into the path /Deck/*

Describe alternatives you've considered
Disabeling Deck, but that isn't what I want.

Additional context
Please, consider resolving this issue, as me, and most likely many other people would like to enable Deck for guests

Steps to reproduce are in the comments

No files, tests, or entry points are named. Start by reviewing how Deck settings expose the folder path and how Deck saves files for guest accounts; clarify whether the goal is an in-app setting, a default /Deck path, or both. Done means guest users no longer expose Deck files directly in / and the chosen path behavior is covered by relevant tests.