Sign-out dialog without key backup looks somewhat odd

### Steps to reproduce

1. Sign into an existing account
2. Don't set up key backup
3. Sign out again
4. Notice that the sign-out dialog is somewhat oddly arranged

### Outcome

#### What did you expect?

The dialog to be intuitive and well aligned.

#### What happened instead?

* The vertical whitespace above the buttons feels quite large
* The vertical whitespace between the buttons and the "Advanced" expander feels quite small
* The buttons are right aligned while the "Advanced" expander is left aligned
* The expander only hides a single button
* That button is left aligned
* The vertical spacing between the "Advanced" label and the button below it is larger than the spacing between the label and the buttons above it


### Operating system

fedora Linux 40

### Browser information

Firefox 128.0.3

### URL for webapp

app.element.io

### Application version

Element version: 1.11.73 Crypto version: Rust SDK 0.7.1 (431263d), Vodozemac 0.6.0

### Homeserver

matrix.org

### Will you send logs?

No