fix(qt): elevated controls lift on hover instead of darkening

Buttons that rest on surfaceElevated used surfaceHover for their hover
fill: a 6% white wash meant for rows that rest transparent. Over an
elevated button it lands DARKER than the rest fill — on a modal's dark
ground the Cancel/Save/footer buttons went near-black under the pointer.

QbzTheme gains surfaceElevatedHover (a lift of surfaceElevated, derived
so every palette has it), its ambient half-alpha twin, and the
elevatedFill / elevatedHoverFill pair an ambient-aware control paints.
Every site with the old pairing (65 across modals, toolbars, selects,
circle actions, chips and cards) now hovers to the lift.

cc

crates/qbz-qt/qml/controls/QbzConfirmModal.qml

@@ -220,7 +220,7 @@ Item {
                         width: cancelLbl.implicitWidth + 32
                         height: root.kioskHost ? 44 : 36
                         radius: theme.radiusSm
-                        color: cancelArea.containsMouse ? theme.surfaceHover
+                        color: cancelArea.containsMouse ? theme.surfaceElevatedHover
                                                         : theme.surfaceElevated
                         activeFocusOnTab: root.opened
                         border.width: activeFocus ? 2 : 0