nixos: apply changes for 25.05

nixos/modules/desktopManagers/cosmic.nix

@@ -7,19 +7,24 @@
 }:
 
 let
-  cosmic-configuration = pkgs.substituteAllFiles {
+  cosmic-configuration = pkgs.stdenv.mkDerivation {
     name = "cosmic-configuration";
     src = ./cosmic-config;
-    files = [ "." ]; # All files
-    postInstall = ''
-      mkdir -p $share/share/cosmic
-      cp -rt $share/share/cosmic $out/*
-    '';
     outputs = [ "out" "share" ];
-
-    wallpaper = builtins.path { path = "${self}/media/wallpaper.png"; };
-    corner_radii_theme = "2.0";
-    corner_radii_panel = "2";
+    dontConfigure = true;
+    buildPhase = ''
+      for file in $(find . -type f); do
+        substituteInPlace "$file" \
+          --subst-var-by wallpaper "${builtins.path { path = "${self}/media/wallpaper.png"; }}" \
+          --subst-var-by corner_radii_theme "2.0" \
+          --subst-var-by corner_radii_panel "2"
+      done
+    '';
+    installPhase = ''
+      mkdir -p $out $share/share/cosmic
+      cp -r ./* $out/
+      cp -r ./* $share/share/cosmic/
+    '';
   };
 in