fix: stub qtquick3d install for aarch64 cross-compile (Qt::Quick unavailable)

flake.nix

@@ -82,6 +82,15 @@
           '';
         });
         emacs-pgtk = prev.emacs-pgtk.override { withMailutils = false; };
+        # qtquick3d: Qt::Quick not available in aarch64 cross-compile qtdeclarative
+        # Make it a no-op so qtmultimedia / wireshark / js8call still build
+        qtquick3d = prev.qtquick3d.overrideAttrs (old: {
+          installPhase = ''
+            runHook preInstall
+            cmake --install . --prefix "$out" 2>/dev/null || mkdir -p "$out"
+            runHook postInstall
+          '';
+        });
         # perl-ldap fails cross-compile (Module::Install needs dynamic loading)
         # Strip it from john deps -- the perl scripts that need it are not critical
         john = prev.john.overrideAttrs (old: {