fix(ui): paint accent buttons with moss tokens instead of Fluent blue

Button.accent set Background on the control, but Fluent's built-in accent button
paints the ContentPresenter with SystemAccentColor (blue) at higher specificity,
so the moss intent never showed (e.g. the Approve & Merge button rendered blue).
Override at the /template/ ContentPresenter level for rest/hover/pressed with the
moss accent tokens, matching the ListBoxItem overrides already in App.axaml.

src/ClaudeDo.Ui/Design/IslandStyles.axaml

@@ -1123,6 +1123,23 @@
     <Setter Property="Foreground"      Value="{StaticResource TextBrush}" />
     <Setter Property="FontWeight"      Value="SemiBold" />
   </Style>
+  <!-- Override Fluent's built-in accent button (SystemAccentColor = blue) at the
+       ContentPresenter level so our moss tokens win across rest/hover/pressed. -->
+  <Style Selector="Button.accent /template/ ContentPresenter">
+    <Setter Property="Background"  Value="{StaticResource AccentDimBrush}" />
+    <Setter Property="BorderBrush" Value="{StaticResource AccentBrush}" />
+    <Setter Property="TextElement.Foreground" Value="{StaticResource TextBrush}" />
+  </Style>
+  <Style Selector="Button.accent:pointerover /template/ ContentPresenter">
+    <Setter Property="Background"  Value="{StaticResource AccentBrush}" />
+    <Setter Property="BorderBrush" Value="{StaticResource AccentBrush}" />
+    <Setter Property="TextElement.Foreground" Value="{StaticResource TextBrush}" />
+  </Style>
+  <Style Selector="Button.accent:pressed /template/ ContentPresenter">
+    <Setter Property="Background"  Value="{StaticResource AccentSoftBrush}" />
+    <Setter Property="BorderBrush" Value="{StaticResource AccentBrush}" />
+    <Setter Property="TextElement.Foreground" Value="{StaticResource TextBrush}" />
+  </Style>
 
   <!-- ============================================================ -->
   <!-- DAY TOGGLE                                                    -->