fix(settings): harden migration and accessibility

Apply interface scaling through Qt at startup, complete keyboard navigation, move account migration into setup and progress modals, and defer Subsonic sync while the server scans.

cx

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

@@ -20,8 +20,24 @@ Rectangle {
     height: 18
     radius: 4
     color: root.checked ? theme.accent : "transparent"
-    border.width: root.checked ? 0 : 2
-    border.color: theme.textMuted
+    border.width: root.activeFocus ? 2 : (root.checked ? 0 : 2)
+    border.color: root.activeFocus
+        ? (root.checked ? theme.accentGlyphColor : theme.accent)
+        : theme.textMuted
+    activeFocusOnTab: root.enabled
+    Accessible.role: Accessible.CheckBox
+    Accessible.checked: root.checked
+    Accessible.onToggleAction: if (root.enabled) root.toggled()
+
+    Keys.onPressed: function (event) {
+        if (root.enabled && !event.isAutoRepeat
+                && (event.key === Qt.Key_Space
+                    || event.key === Qt.Key_Return
+                    || event.key === Qt.Key_Enter)) {
+            root.toggled()
+            event.accepted = true
+        }
+    }
 
     QbzIcon {
         anchors.centerIn: parent
@@ -46,6 +62,7 @@ Rectangle {
     MouseArea {
         anchors.fill: parent
         cursorShape: Qt.PointingHandCursor
+        onPressed: root.forceActiveFocus()
         onClicked: root.toggled()
     }
 }