Fix jellyfinScaleFactor implementation in kodi role

The original implementation had several issues that prevented it from
building:
- Used buildInputs instead of nativeBuildInputs for makeWrapper
- Referenced wrong executable name (jellyfinmediaplayer vs jellyfin-desktop)
- Used wrapProgram which doesn't work with symlinks from symlinkJoin

Fixed by using makeWrapper directly with the correct executable path
after removing the symlink.

Also enabled jellyfinScaleFactor = 1.5 on boxy for UI scaling.

machines/boxy/configuration.nix

@@ -26,6 +26,7 @@ with lib;
       enable = true;
       autologin = true;
       wayland = true;
+      jellyfinScaleFactor = 1.5;
     };
     users.enable = true;
   };