fix(nix): replace pkgs.system with hostPlatform.system

[DivitMittal]

Summary

• Fixes Nix evaluation warning by replacing deprecated pkgs.system with hostPlatform.system
• Aligns with Nix best practices and modern attribute naming

Details

Nix has deprecated pkgs.system in favor of stdenv.hostPlatform.system. This PR updates the home-manager module to use the correct hostPlatform.system attribute that's already available in the function parameters.

Change: Line 22 in nix/hmModule.nix

- package = mkPackageOption self.packages.${pkgs.system} "kanata-tray" { nullable = true; };
+ package = mkPackageOption self.packages.${hostPlatform.system} "kanata-tray" { nullable = true; };

This resolves the evaluation warning:

trace: evaluation warning: 'system' has been renamed to/replaced by 'stdenv.hostPlatform.system'