tokenise window-control colours + palette shadow

Hard-coded Windows close-button red (#E81123), white close glyph, and
the palette's 0x40000000 drop shadow were the three colour sites the
UX consultant flagged as not adapting per theme. Now they're
`windowControl.closeHoverBackground` / `closeHoverForeground` /
`shadow.ambient`. Paper themes override the shadow to a softer ink so
it doesn't read as a CRT halo on cream.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/widgets/src/clide_column_hat.dart

@@ -108,7 +108,7 @@ class _WinButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final hoverBg = isClose ? const Color(0xFFE81123) : tokens.listItemHoverBackground;
+    final hoverBg = isClose ? tokens.windowControlCloseHoverBackground : tokens.listItemHoverBackground;
     return ClideTappable(
       onTap: onTap,
       builder: (context, hovered, _) => Container(
@@ -116,7 +116,11 @@ class _WinButton extends StatelessWidget {
         height: hatHeight,
         color: hovered ? hoverBg : null,
         alignment: Alignment.center,
-        child: ClideIcon(icon, size: 14, color: hovered && isClose ? const Color(0xFFFFFFFF) : tokens.globalTextMuted),
+        child: ClideIcon(
+          icon,
+          size: 14,
+          color: hovered && isClose ? tokens.windowControlCloseHoverForeground : tokens.globalTextMuted,
+        ),
       ),
     );
   }

lib/widgets/src/clide_palette.dart

@@ -126,11 +126,11 @@ class _ClidePaletteState extends State<ClidePalette> {
                   color: tokens.dropdownBackground,
                   border: Border.all(color: tokens.dropdownBorder),
                   borderRadius: BorderRadius.circular(6),
-                  boxShadow: const [
+                  boxShadow: [
                     BoxShadow(
-                      color: Color(0x40000000),
+                      color: tokens.shadowAmbient,
                       blurRadius: 12,
-                      offset: Offset(0, 4),
+                      offset: const Offset(0, 4),
                     ),
                   ],
                 ),