Feature: Auto-switch between preview and details based on preview availability

### What feature or improvement do you think would benefit Files?

Right now you have to manually toggle between Preview and Details. It’d be great if Files could auto-switch based on what’s selected:
- Files with a valid preview → show Preview Pane
- Files without preview → fall back to Details Pane
- Folders → always show Details Pane (since previews don’t make sense there)

This would save clicks, avoid empty preview panes, and make navigation feel smoother. Ideally, there could be a setting to turn this auto-switch on/off for people who prefer manual control.

### Requirements

- This proposal will accomplish eliminating empty/meaning-less preview panes
- This proposal will accomplish smoother navigation without wasted clicks
- This proposal will accomplish creating a smarter, adaptive experience that keeps the interface clean and always relevant to the content you’re working with.

### Files Version

4.1.1.0

### Windows Version

10.0.26200.8457

### Comments

_No response_