Here's what it looks like now:
Verifications performed:
- There are no actual settings changes for any users, since browsers ask to set themselves as the default, and distros ship config files already specifying their preferred browser.
- Changing the browser in the combobox correctly updates both `~/.config/kdeglobals` and `~/.configmimeapps.list`
- The combobox's default setting is now correctly identical to what `~/.config/mimeapps.list` specifies, if anything
- KRun still does unnecessary URL introspection when there is in fact a default browser set in `~/.config/mimeapps.list` but ~/.config/kdeglobals` doesn't have a default browser set, which is fixed separately in KIO with D17371