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/QbzSelect.qml

@@ -74,8 +74,8 @@ Rectangle {
     // shows through the control (QbzSelect.slint:110-116). Hover keeps its own
     // token, which is already translucent.
     color: selArea.containsMouse && enabled
-        ? theme.surfaceHover
-        : (theme.ambientOn ? theme.surfaceElevatedA50 : theme.surfaceElevated)
+        ? theme.elevatedHoverFill
+        : theme.elevatedFill
     opacity: enabled ? 1.0 : 0.4
     activeFocusOnTab: enabled
     Accessible.role: Accessible.ComboBox