If the "create account" screen is closed before you validate your email, the account is not created.

### Steps to reproduce

1. Try to register in EW
2. Close the "create account" window while it's on the "validating" stage
3. Validate the link in your email
4. Discover your account is silently not created at all

c.f. https://blog.koehntopp.info/2024/02/13/the-matrix-trashfire.html

### Outcome

#### What did you expect?

As a workaround, warn the user massively that they shouldn't close the window.

In general, we shouldn't be relying on keeping the window open at all.

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

_No response_

### Application version

v1.11.58

### Homeserver

_No response_

### Will you send logs?

No