[25.05] zeal: migrate to pkgs/by-name, use qt6#439086

wolfgangwalther merged 1 commit intoNixOS:release-25.05NixOS/nixpkgs:release-25.05from

fabianhjr:backport-zeal-manualfabianhjr/nixpkgs:backport-zeal-manualCopy head branch name to clipboard