Vulkan layer that swaps vrcompositor's stream distortion shader for a
chroma-keyed variant so the Frame's passthrough camera shows through a
solid-colour background. Includes the in-headset dashboard panel (on/off,
key colour, similarity/softness/spill, desktop background key colour vs
mountains), the PC background sync helper, the PC eyedropper panel, and
install/uninstall scripts.
