Using the same name as an existing calendar _deleted_ the original calendar/task list

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Describe the bug
Started a Personal deck, with my primary calendar named Personal and a task list as Personal. This deleted the original calender somehow in the migration/removal of a task list of the same name, and once the Deck name changed, somehow the Personal account was lost my-instance-of-nextcloud.com/remote.php/dav/calendars/user/personal/ was a 404 at first or mobile (DAVx5), and then reappeared on the webapp. 🤷

All data seems to be lost 😭

To Reproduce
Steps to reproduce the behavior:

1. create a deck with the same name as an exiting calendar / task
2. delete the task list
3. calendar is also removed
4. Deck remains

Expected behavior
NEVER straight loose data based on a name conflict, without warning. No way to undo/recover.

Start by reproducing the reported sequence: create a Deck with the same name as an existing calendar or task list, delete the task list, and check whether the calendar remains. Trace the Deck task-list migration/removal path and its handling of name conflicts. Done means the existing calendar and its data are preserved, with a warning or recovery path when names conflict.