Upgrade NixOS to 25.11 and fix Jovian module organization

- Update flake inputs from 25.05 to 25.11 (nixpkgs, home-manager, nix-darwin)
- Remove Jovian compatibility shim that's no longer needed
- Move SteamOS configuration to only import in nix-deck machine
- Fixes jovian module not found error during nixos-rebuild

roles/desktop/default.nix

@@ -22,6 +22,5 @@ with lib;
     ./kde.nix
     ./programs.nix
     ./sddm.nix
-    ./steamos.nix
   ];
 }

roles/jovian-compat.nix

@@ -1,64 +0,0 @@
-{ lib, config, ... }:
-
-# Minimal Jovian compatibility layer for NixOS stable (25.05)
-# Defines only the Jovian options used by roles/desktop/steamos.nix
-# No actual implementation - just option definitions to prevent evaluation errors
-# REMOVE THIS FILE when all systems are on NixOS 25.11+ or unstable
-
-with lib;
-
-let
-  nixosVersion = config.system.nixos.release;
-  isCompatibleVersion = versionOlder nixosVersion "25.11";
-in
-{
-  options.jovian = {
-    steam = {
-      enable = mkEnableOption "Steam (jovian-compat stub)";
-
-      autoStart = mkOption {
-        type = types.bool;
-        default = false;
-        description = "Auto-start Steam (jovian-compat stub)";
-      };
-
-      user = mkOption {
-        type = types.str;
-        default = "user";
-        description = "Steam user (jovian-compat stub)";
-      };
-
-      desktopSession = mkOption {
-        type = types.nullOr types.str;
-        default = null;
-        description = "Desktop session (jovian-compat stub)";
-      };
-    };
-
-    decky-loader = {
-      enable = mkEnableOption "Decky Loader (jovian-compat stub)";
-    };
-  };
-
-  config = mkMerge [
-    {
-      assertions = [
-        {
-          assertion = isCompatibleVersion;
-          message = ''
-            The Jovian compatibility shim (roles/jovian-compat.nix) is only needed for NixOS 25.05 and earlier.
-            You are running NixOS ${nixosVersion}.
-            Please remove 'roles/jovian-compat.nix' from your flake.nix nixosModules list.
-          '';
-        }
-      ];
-    }
-    # No config implementation - these options do nothing on stable systems
-    # steamos role is only enabled on nix-deck which uses unstable anyway
-    (mkIf config.jovian.steam.enable {
-      warnings = [
-        "Jovian is enabled but you're using the compatibility stub. This won't work correctly. Use NixOS unstable for Jovian support."
-      ];
-    })
-  ];
-}