Fall back to plain files when mknod is unavailable

[LoneAngelFayt]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

Adds an elif branch to the gamepad block in init-selkies-config/run that falls back to plain files when mknod is not available, gated on touch /dev/input/js0 the same way the existing block is gated on mknod /dev/input/js0.

Benefits of this PR and context:

Under rootless podman there is no CAP_MKNOD, and the kernel refuses device nodes inside a userns anyway, so the mknod fails and the whole block drops to the else branch. That sets SELKIES_GAMEPAD_ENABLED=false and never writes LD_PRELOAD into container_environment, so gamepads are dead in every app and nothing logs why.

Empty files are enough here because the joystick interposer hooks open() on the path name and the fake libudev handles enumeration, so nothing ever opens the real node.

How Has This Been Tested?

Rootless podman on Fedora 43, running the webstation image. Before the change /dev/input is empty and /run/s6/container_environment/LD_PRELOAD does not exist. After it, the js/event files are created, LD_PRELOAD is set, and the gamepad env vars stay at their defaults. Verified controller input reaching PCSX2 through the browser, with connections on /tmp/selkies_js*.sock.

Also checked the rootful path is untouched: with mknod available the first branch still wins and the elif never runs.

Source / References:

n/a

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