preview panel takes over window

### What Happened?

When clicking a file with a small Files window, the preview panel shoves the rest of the folder's contents to an unusable sliver

### Steps to Reproduce

https://github.com/user-attachments/assets/a036a65e-e3d2-4dfb-ad70-659c960083a5

### Expected Behavior

It should take up half width at most

### OS Version

8.x (Circe)

### OS Architecture

amd64 (on most hardwares)

### Session Type

Secure Session (Wayland, This is the default)

### Software Version

Latest release (I have run all updates)

### Log Output

```shell

```

### Hardware Info

_No response_

Reproduce the issue in elementary Files on OS 8.x by opening a small Files window and selecting a file to show the preview panel. Inspect the preview panel sizing behavior in the Files code and ensure the panel uses no more than half the window width while the folder contents remain usable.

Written by the indexing model from the issue text.