implement a state check function

Being able to validate FT application state would help increase the reliability in the server behavior. Should see what properties can be checked to find the following:

- FT is open/in focus
- FT is in a call lobby (pre-join)
- FT is in a call, with sidebar closed
- FT is in a call, with the sidebar open (this is preferable)

This could be then used to validate calls are joined/left correctly, as well as determine if APIs are being called in the right order.

No file, test, or entry point is named. Start by examining how the Go server interacts with the FaceTime application and the available AppleScript state, then define checks for focus, pre-join, and call states with the sidebar status. Done means the server can reliably distinguish these states and use them to validate call sequencing.

Written by the indexing model from the issue text.