PeaZip: Qt6 everywhere except GNOME/XFCE (GTK3 build is upstream alpha)

YuKu tested gtk3 on niri: broken UI until a manual swap to qt6 fixed
it. Upstream's own changelog: the GTK3 package is 'for test purpose
only' (Lazarus GTK3 widgetset is alpha) and Qt6 supersedes Qt5.

New mapping: gtk3 ONLY for genuine GTK stacks (gnome, xfce); qt6 for
everything else - plasma, hyprland, niri, mangowc, chadwm (Qt6 handles
Wayland and X11 cleanly).

Harness: full DE/TWM matrix passes (7/7); existing qt5 on niri now
swaps to qt6 (not gtk3); a machine already on qt6 (YuKu's laptop
after the manual swap) is a clean no-op.

setup.sh

@@ -647,11 +647,17 @@ info "Tailoring toolkits for DE=$DE / TWM=$TWM..."
 #   right flavor   -> nothing to do
 #   OTHER flavor   -> dnf SWAP to the wanted one (atomic: on failure the
 #                     existing flavor stays, which is the safe outcome)
-if [[ "$DE" == "plasma" || "$TWM" == "hyprland" ]]; then
-    peazip_wanted="peazip-qt6"
-else
-    # XFCE, GNOME, Niri, MangoWC, chadwm: lightweight/generic toolkits
+#
+# Flavor choice: PeaZip's GTK3 build is ALPHA (Lazarus GTK3 widgetset) —
+# upstream ships it "for test purpose only", and it renders broken on
+# non-GTK Wayland compositors (YuKu-proven on niri: broken UI until a
+# manual swap to qt6). GTK3 therefore only for genuine GTK stacks
+# (GNOME, XFCE); Qt6 everywhere else — including niri/MangoWC/Hyprland
+# and chadwm (Qt6 handles both Wayland and X11 cleanly).
+if [[ "$DE" == "gnome" || "$DE" == "xfce" ]]; then
     peazip_wanted="peazip-gtk3"
+else
+    peazip_wanted="peazip-qt6"
 fi
 peazip_existing=""
 local_v=""