Enhancement: One image picker everywhere

Every image field in the app now opens the same browse picker, so you choose images from your uploaded files instead of pasting URLs by hand.

What's new. Wherever a component asks for an image (banners, image components, callouts, radio option images and more), you'll now find a browse button that opens your image library. Radio option images also show a thumbnail preview once selected, so you can see at a glance what each option will display.

Fixes along the way. The image picker no longer opens behind the appearance settings window, a duplicated image field was removed from one of the content forms, and the styling menu's buttons now use consistent capitalisation.

Existing setups. Image URLs you've already saved keep working exactly as before. The picker is simply an easier way to set them.