desktop-jovian: unify steam/jovian config across yarn + patiodeck

- modules/desktop-jovian.nix: shared Jovian deck-mode config (unfree
  predicate, jovian.steam, sddm, gamescope override, imports
  desktop-steam-update.nix)
- home/progs/steam-shortcuts.nix: declarative non-Steam shortcuts
  (Prism Launcher); add new entries here for all Jovian hosts
- hosts/yarn/default.nix: reduced to host-specific config only
- hosts/patiodeck/default.nix: same

hosts/yarn/default.nix

@@ -1,5 +1,4 @@
 {
-  config,
   pkgs,
   lib,
   username,
@@ -10,14 +9,13 @@
 {
   imports = [
     ../../modules/desktop-common.nix
-    ../../modules/desktop-steam-update.nix
+    ../../modules/desktop-jovian.nix
     ../../modules/no-rgb.nix
     ./disk.nix
     ./impermanence.nix
     ./vr.nix
 
     inputs.impermanence.nixosModules.impermanence
-    inputs.jovian-nixos.nixosModules.default
   ];
 
   fileSystems."/media/games" = {
@@ -84,31 +82,6 @@
 
   systemd.services.lactd.serviceConfig.ExecStartPre = "${lib.getExe pkgs.bash} -c \"sleep 3s\"";
 
-  nixpkgs.config.allowUnfreePredicate =
-    pkg:
-    builtins.elem (lib.getName pkg) [
-      "steamdeck-hw-theme"
-      "steam-jupiter-unwrapped"
-      "steam"
-      "steam-original"
-      "steam-unwrapped"
-      "steam-run"
-    ];
-
-  jovian = {
-    devices.steamdeck.enable = false;
-    steam = {
-      enable = true;
-      autoStart = true;
-      desktopSession = "niri";
-      user = username;
-    };
-  };
-
-  # Jovian-NixOS requires sddm
-  # https://github.com/Jovian-Experiments/Jovian-NixOS/commit/52f140c07493f8bb6cd0773c7e1afe3e1fd1d1fa
-  services.displayManager.sddm.wayland.enable = true;
-
-  # Disable gamescope from common.nix to avoid conflict with jovian-nixos
-  programs.gamescope.enable = lib.mkForce false;
+  # yarn is not a Steam Deck
+  jovian.devices.steamdeck.enable = false;
 }