dolphin: fix file associations not working

nixos/configuration.nix

@@ -94,10 +94,6 @@
     description = "Khaïs COLIN";
     extraGroups = [ "networkmanager" "wheel" ];
     shell = pkgs.zsh;
-    packages = with pkgs; [
-      kdePackages.kate
-    #  thunderbird
-    ];
   };
 
   users.users.guest = {
@@ -135,6 +131,10 @@
     wluma
     # man pages
     man-pages man-pages-posix
+    # kde
+    kdePackages.kate kdePackages.plasma-workspace kdePackages.dolphin
+    # fix kde apps having no icons
+    kdePackages.qtsvg
   ];
 
   # set global environment variables
@@ -142,6 +142,8 @@
     # I don't know what this does, but it is needed for wluma to work correctly.
     # It will also slightly increase cpu usage (on wayland compositors), but shouldn't be too bad.
     WLR_DRM_NO_MODIFIERS = 1;
+    # fix dolphin file associations not working
+    XDG_MENU_PREFIX = "plasma-";
   };
 
   # Some programs need SUID wrappers, can be configured further or are