Add ensure fs_loading_screen at the top of server.cfg (before other resources).
Configuration
Tweak background, text, and layout in app/app.html and app/app.css.
Replace the audio in assets/music.mp3 (keep the name or update the path in app/app.js).
Default volume and controls live in app/app.js (setVolume(50)).
To disable music, remove the audio.play() call or set audio.volume = 0.
Swap branding assets in the assets/ folder.
Tips
If you need to manually close the loadscreen after character load, call ShutdownLoadingScreenNui() from another script (the loadscreen stays until progress reaches 100%).