polkit-kde-agent: throw the correct package name for qt6 (#387951)

pkgs/top-level/aliases.nix

@@ -58,7 +58,7 @@ let
       marble merkuro milou minuet okular oxygen oxygen-icons5 picmi
       plasma-browser-integration plasma-desktop plasma-integration plasma-nano
       plasma-nm plasma-pa plasma-mobile plasma-systemmonitor plasma-thunderbolt
-      plasma-vault plasma-workspace plasma-workspace-wallpapers polkit-kde-agent
+      plasma-vault plasma-workspace plasma-workspace-wallpapers
       powerdevil qqc2-breeze-style sddm-kcm skanlite skanpage spectacle
       systemsettings xdg-desktop-portal-kde yakuake zanshin
       ;
@@ -1180,6 +1180,14 @@ mapAliases {
   plots = throw "'plots' has been replaced by 'gnome-graphs'"; # Added 2025-02-05
   pltScheme = racket; # just to be sure
   poac = cabinpkg; # Added 2025-01-22
+  polkit-kde-agent = throw ''
+    The top-level polkit-kde-agent alias has been removed.
+
+    Please explicitly use kdePackages.polkit-kde-agent-1 for the latest Qt 6-based version,
+    or libsForQt5.polkit-kde-agent for the deprecated Qt 5 version.
+
+    Note that Qt 5 versions of most KDE software will be removed in NixOS 25.11.
+  ''; # Added 2025-03-07
   poretools = throw "poretools has been removed from nixpkgs, as it was broken and unmaintained"; # Added 2024-06-03
   powerdns = pdns; # Added 2022-03-28
   projectm = throw "Since version 4, 'projectm' has been split into 'libprojectm' (the library) and 'projectm-sdl-cpp' (the SDL2 frontend). ProjectM 3 has been moved to 'projectm_3'"; # Added 2024-11-10