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/views/LocalAlbumView.qml

@@ -588,7 +588,7 @@ Rectangle {
                         border.width: 1
                         border.color: root.multiSelect ? theme.accent : theme.borderSubtle
                         color: (root.multiSelect || selectArea.containsMouse)
-                            ? theme.surfaceHover
+                            ? theme.surfaceElevatedHover
                             : theme.surfaceElevated
                         QbzIcon {
                             name: "square-check-big"