Add Linux graphics and environment profiles

[SaicharanKandukuri]

• Adds selectable software, Zink, VirGL, VirGL ANGLE, and experimental Venus profiles.
• Applies graphics and environment settings automatically to terminals, apps, and desktops.
• Adds VirGL compatibility and multi-client modes with safe compositor defaults.
• Adds editable per-system environment variables with resettable uDroid defaults.
• Adds per-distro Android compatibility mounts and private shared memory for blocked Linux paths.
• Passes unit tests, runtime asset verification, and the dev APK build; verified on the connected Pixel.
• Stacked on Improve desktop touch input and process warnings #27.