feat(ui): accent color presets in Settings → General

Adds Moss / Peat / Sea preset swatches to the General settings tab.
Selecting a preset mutates the live SolidColorBrush objects in the
Application resource dictionary so all StaticResource consumers update
instantly; the choice is persisted to ui.config.json and re-applied
at startup. Missing or unknown saved value falls back to Moss.

src/ClaudeDo.Ui/Views/Modals/SettingsModalView.axaml

@@ -2,6 +2,7 @@
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="using:ClaudeDo.Ui.ViewModels.Modals"
         xmlns:settings="using:ClaudeDo.Ui.ViewModels.Modals.Settings"
+        xmlns:ui="using:ClaudeDo.Ui"
         xmlns:agent="using:ClaudeDo.Ui.ViewModels.Agent"
         xmlns:services="using:ClaudeDo.Ui.Services"
         xmlns:ctl="using:ClaudeDo.Ui.Views.Controls"
@@ -61,6 +62,39 @@
                   </ComboBox.ItemTemplate>
                 </ComboBox>
               </StackPanel>
+              <StackPanel Spacing="4">
+                <TextBlock Classes="field-label" Text="{loc:Tr settings.general.accentPreset}"/>
+                <ItemsControl ItemsSource="{Binding General.AccentPresetSwatches}">
+                  <ItemsControl.ItemsPanel>
+                    <ItemsPanelTemplate>
+                      <StackPanel Orientation="Horizontal" Spacing="8"/>
+                    </ItemsPanelTemplate>
+                  </ItemsControl.ItemsPanel>
+                  <ItemsControl.ItemTemplate>
+                    <DataTemplate x:DataType="ui:AccentPresetSwatchViewModel">
+                      <Button Padding="6,4"
+                              Command="{Binding $parent[ItemsControl].((vm:SettingsModalViewModel)DataContext).General.SelectAccentPresetCommand}"
+                              CommandParameter="{Binding Preset}">
+                        <StackPanel Spacing="4">
+                          <Grid Width="32" Height="32">
+                            <Border Width="32" Height="32" CornerRadius="16"
+                                    BorderBrush="{DynamicResource AccentBrush}" BorderThickness="2"
+                                    IsVisible="{Binding IsSelected}"/>
+                            <Ellipse Width="22" Height="22"
+                                     HorizontalAlignment="Center" VerticalAlignment="Center">
+                              <Ellipse.Fill>
+                                <SolidColorBrush Color="{Binding DisplayColor}"/>
+                              </Ellipse.Fill>
+                            </Ellipse>
+                          </Grid>
+                          <TextBlock Text="{Binding DisplayName}"
+                                     HorizontalAlignment="Center" FontSize="11"/>
+                        </StackPanel>
+                      </Button>
+                    </DataTemplate>
+                  </ItemsControl.ItemTemplate>
+                </ItemsControl>
+              </StackPanel>
               <StackPanel Spacing="4">
                 <TextBlock Classes="field-label" Text="{loc:Tr settings.general.defaultInstructions}"/>
                 <TextBox AcceptsReturn="True" TextWrapping="Wrap" Height="110"