The URL is configurable in settings, so you could fork the app loader, change it to be exactly how you want it (if that's deleting everything and replacing it with one big text box that would work fine, but you could do much more), and then change the URL in Gadgetbridge to your version hosted on GitHub pages and you're sorted.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
One option for you is Gadgetbridge loads the 'App Loader', which is basically this file: https://github.com/espruino/BangleApps/blob/master/android.html
The URL is configurable in settings, so you could fork the app loader, change it to be exactly how you want it (if that's deleting everything and replacing it with one big text box that would work fine, but you could do much more), and then change the URL in Gadgetbridge to your version hosted on GitHub pages and you're sorted.