fix(qt): stop shadowing Item.enabled and Item.palette in four components

SettingsButton, QbzToggle and QbzSelect declared their own `enabled` over
Item's, and ReactiveRingsPanel its own `palette` over Item's QPalette: Qt
flagged all four at start (propertyCache: "overrides a member of the base
object"). The shadowed `enabled` never disabled input by itself — each
control filtered clicks and keys by hand, and any child that did not would
have kept receiving events. The inherited property now drives the visuals,
the focus policy and the guards, and disables the subtree the way Item
does; the rings' colour list is `ringPalette`.

cc

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

@@ -26,7 +26,6 @@ Rectangle {
     // window edge may opt into a lateral list without changing every other
     // QbzSelect instance. Supported values: "below" and "left".
     property string popupPlacement: "below"
-    property bool enabled: true
     property bool searchable: false
     // Bootstrap-style small variant (QbzSelect.slint:74-76). The default is the
     // standard Settings size; TOOLBARS opt in with `sm: true` — 30px tall, r6,

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

@@ -14,7 +14,6 @@ Rectangle {
     id: root
 
     property bool checked: false
-    property bool enabled: true
     signal toggled(bool value)
 
     QbzTheme { id: theme }

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

@@ -20,7 +20,6 @@ Rectangle {
     property string trailingIconName: ""
     property bool danger: false
     property bool busy: false
-    property bool enabled: true
     // The two metrics the MyQBZ modal footers and the Disco builder need. The
     // Slint's SecondaryButton is 34px/min-160 in Settings and 38px/hug in a
     // modal footer, which is one control with two call-site numbers — not two

crates/qbz-qt/qml/immersive/ReactiveRingsPanel.qml

@@ -53,7 +53,9 @@ Rectangle {
     readonly property color primaryColor: QbzShell.ambientPrimary
     readonly property color accentColor: QbzShell.ambientAccent
     readonly property color secondaryColor: QbzShell.ambientSecondary
-    readonly property var palette: [
+    // `ringPalette`, not `palette`: Item already owns a `palette` (QPalette)
+    // and shadowing it drew a propertyCache warning on every start.
+    readonly property var ringPalette: [
         root.primaryColor,
         root.accentColor,
         root.secondaryColor,
@@ -65,15 +67,15 @@ Rectangle {
     readonly property var bandNames: ["SUB", "BASS", "MID", "PRES", "AIR"]
 
     function paletteColor(position, alpha) {
-        var count = root.palette.length
+        var count = root.ringPalette.length
         var wrapped = position % count
         if (wrapped < 0)
             wrapped += count
         var lo = Math.floor(wrapped)
         var hi = (lo + 1) % count
         var mix = wrapped - lo
-        var a = Qt.lighter(root.palette[lo], 1.0)
-        var b = Qt.lighter(root.palette[hi], 1.0)
+        var a = Qt.lighter(root.ringPalette[lo], 1.0)
+        var b = Qt.lighter(root.ringPalette[hi], 1.0)
         return Qt.rgba(a.r + (b.r - a.r) * mix,
                        a.g + (b.g - a.g) * mix,
                        a.b + (b.b - a.b) * mix,
@@ -181,7 +183,7 @@ Rectangle {
                     "speed": 0.006 + intensity * 0.013,
                     "color": root.nextColor
                 })
-                root.nextColor = (root.nextColor + 1) % root.palette.length
+                root.nextColor = (root.nextColor + 1) % root.ringPalette.length
                 if (next.length > root.maxPulseRings)
                     next.shift()
             }