UserB can view UserA's conversation cards after creating an account

### Describe the bug

A UserB that just created an account after finishing the quiz from a link he received can view the conversation cards of UserA.

### To Reproduce

1. You start a new conversation and paste the link into a new tab.
2. You complete the quiz and click through all pages until you can create an account at the end.
3. After creating the account you're logged in as UserB.
4. If you now go to the conversation drawer, you can see the conversation cards from UserA (as you just created a new account, there should be only one conversation card from UserA).

### Expected behavior

After you created the account and are logged in, your conversation drawer should only show you one card, which is the conversation that lead to creating the account with UserA.

### Task

- I would guess that this has to do with the quizId that is stored in the localStorage.

Reproduce the account-creation flow, then inspect the conversation drawer and the localStorage quizId handling mentioned in the task. Done means a newly created UserB sees only the conversation that led to account creation, not UserA's other conversation cards.

Written by the indexing model from the issue text.