Add Steam Deck (nix-deck) configuration with Jovian-NixOS and remote building

- Add Jovian-NixOS integration for Steam Deck hardware support
- Create nix-deck machine configuration with SteamOS role
- Add jovian-compat.nix for NixOS 25.05 compatibility (remove in 25.11+)
- Create remote-build role for distributed builds
- Configure zix790prors as build host
- Configure nix-book and nix-deck to use remote builder with fallback
- Add comprehensive setup documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

roles/desktop/default.nix

@@ -23,5 +23,6 @@ with lib;
     ./kde.nix
     ./programs.nix
     ./sddm.nix
+    ./steamos.nix
   ];
 }