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/kiosk/KioskLocalLibrary.qml

@@ -890,7 +890,7 @@ Rectangle {
         border.width: 1
         border.color: chip.active ? theme.accent : theme.borderSubtle
         color: chip.active ? theme.accent
-             : chipArea.containsMouse ? theme.surfaceHover : theme.surfaceElevated
+             : chipArea.containsMouse ? theme.surfaceElevatedHover : theme.surfaceElevated
         Text {
             id: chipLabel
             anchors.centerIn: parent