Rename the Color singleton to avoid the Qt 6.12 clash

shell/Ui/Button.qml

@@ -32,9 +32,9 @@ BorderSurface {
   property bool bordered: false
 
   // Colors. Defaults track the theme; per-instance overrides are honored.
-  property color foreground: Color.foreground
+  property color foreground: Colors.foreground
   property color background: "transparent"
-  property color accent: Color.accent
+  property color accent: Colors.accent
 
   // Sizing.
   property string fontFamily: Style.font.family
@@ -54,9 +54,9 @@ BorderSurface {
   // Tooltip palette. Auto-rendered if tooltipText is set. Defaults pull
   // from [tooltip] in shell.toml; override per-instance only when a button
   // intentionally wants a tooltip that diverges from the theme.
-  property color tooltipBackground: Color.tooltip.background
-  property color tooltipForeground: Color.tooltip.text
-  property color tooltipBorder: Color.tooltip.border
+  property color tooltipBackground: Colors.tooltip.background
+  property color tooltipForeground: Colors.tooltip.text
+  property color tooltipBorder: Colors.tooltip.border
 
   signal clicked()
   signal rightClicked()
@@ -77,7 +77,7 @@ BorderSurface {
   readonly property bool hot: mouseArea.containsMouse || hasCursor
   readonly property bool _showFocusRing: focusable && activeFocus
   readonly property color _selectedColor: Style.selectedStateColor(root.foreground, root.accent)
-  readonly property var _tooltipBorderSpec: Border.localOrSurfaceSpec("tooltip", "border", root.tooltipBorder, Color.tooltip.border, Math.max(1, Style.normalBorderWidth))
+  readonly property var _tooltipBorderSpec: Border.localOrSurfaceSpec("tooltip", "border", root.tooltipBorder, Colors.tooltip.border, Math.max(1, Style.normalBorderWidth))
   readonly property var _focusBorderSpec: Border.controlSpec("focus", root.foreground, root.accent)
   readonly property var _hoverBorderSpec: Border.controlSpec("hover-cursor", root.foreground, root.accent)
   readonly property var _selectedBorderSpec: Border.controlSpec("selected", root.foreground, root.accent)