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/FolderEditPanel.qml

@@ -180,7 +180,7 @@ Item {
                         radius: 8
                         color: presetTile.active
                             ? theme.accent
-                            : (presetArea.containsMouse ? theme.surfaceHover
+                            : (presetArea.containsMouse ? theme.surfaceElevatedHover
                                                         : theme.surfaceElevated)
                         QbzIcon {
                             anchors.centerIn: parent
@@ -217,7 +217,7 @@ Item {
                     radius: 8
                     color: imageTile.active
                         ? theme.accent
-                        : (imageArea.containsMouse ? theme.surfaceHover
+                        : (imageArea.containsMouse ? theme.surfaceElevatedHover
                                                    : theme.surfaceElevated)
                     // No `clip: true` — it is a rectangular scissor and does
                     // not follow `radius`. RoundedImage masks its own corners.