Knit

Fixes a crash in "Scan their code". The QR scanner has been rebuilt on CameraX. The library it used before could crash the app the moment the camera opened, on devices whose camera reports one frame size and delivers another — which is why it worked on some phones and not others. Decoding now happens in code that treats any unexpected frame as a frame without a code in it, so a scan can no longer take Knit down. The scanner also handles the camera permission properly now: if you decline it, or