Investigate and Support SteamDeck / SteamOS Compatibility

[ruffsl]

Summary:
Initial testing on SteamDeck (SteamOS) shows that while CtrlAssist's virtual device starts and is visible via the list subcommand, it is not detected by the Steam launcher or controller settings. This was tested with a wired Xbox One controller as Assist and the internal SteamDeck gamepad as Primary.

Expected Behavior:
The virtual device should be recognized by Steam's launcher and controller settings, enabling multiplexed input for games running on SteamOS.

Current Behavior:
Virtual device is visible to CtrlAssist but not to Steam's launcher or controller settings. Adding the desktop user to the input GID did not resolve the issue.

Possible Cause:

• SteamOS may have customized udev or input device handling compared to conventional Linux distributions (e.g., NixOS, Ubuntu).
• Additional permissions, device attributes, or integration steps may be required for Steam to recognize virtual devices.

Suggested Solution:

• Investigate SteamOS-specific udev rules, input device handling, and controller integration.
• Compare device visibility and attributes between SteamOS and other Linux distributions where CtrlAssist works.
• Seek contributors with access to SteamDeck hardware and stock SteamOS for further testing and debugging.

Notes:

• SteamDeck support would greatly expand CtrlAssist's user base and accessibility.
• Community contributions and feedback are especially valuable for this issue.

[ruffsl]

With the project now packaged for Flatpak, we should have a easier time finding collaborators to test on SteamOS:

• feat: package CtrlAssist for Flatpak #25