ZEGOCLOUD/zego_uikit_prebuilt_call_example_flutter — reverse-engineered prompt

Build me a simple Flutter video calling demo using ZEGOCLOUD Call Kit. I want it to feel like a small sample app that I can run on two phones and test quickly.

The app should let me enter a user ID and user name, then choose either a 1 to 1 call or a group call. For calls, include both voice and video options if the kit supports it. I also want a call invitation flow, where one user can invite another user into a call and the other person can accept or decline. If offline invitation setup is needed, leave clear placeholders and comments so I know where to add the required keys or config.

Please keep the UI simple and friendly, not fancy. Put the ZEGOCLOUD AppID and AppSign setup in one obvious place. Use the prebuilt call UI as much as possible, including participant list, device controls, view switching, and ringtone support if available.

Look up the current ZEGOCLOUD Flutter docs if you need to.