refactor(ui): share color-coded diff rendering between per-task and combined diff viewers

Extract the unified-diff parser into UnifiedDiffParser and the styled line
renderer into a reusable DiffLinesView control. The combined (planning) diff
now parses its unified-diff string and renders color-coded rows (green
additions / red deletions, file headers) identical to the per-task viewer
instead of dumping plain text into a TextBox.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ClaudeDo.Ui/Views/Controls/DiffLinesView.axaml

@@ -0,0 +1,82 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:ClaudeDo.Ui.ViewModels.Modals"
+             x:Class="ClaudeDo.Ui.Views.Controls.DiffLinesView"
+             x:Name="Root">
+
+  <UserControl.Styles>
+    <!-- diff line row tints via Tag selector (compiled-binding-friendly) -->
+    <Style Selector="Border.diff-line[Tag=add]">
+      <Setter Property="Background" Value="{StaticResource RunningTintBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=del]">
+      <Setter Property="Background" Value="{StaticResource ErrorTintBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=ctx]">
+      <Setter Property="Background" Value="Transparent"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=file]">
+      <Setter Property="Background" Value="{StaticResource Surface3Brush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-sign">
+      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-sign">
+      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-sign">
+      <Setter Property="Foreground" Value="{StaticResource TextFaintBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource TextDimBrush}"/>
+    </Style>
+    <Style Selector="Border.diff-line[Tag=file] TextBlock.diff-text">
+      <Setter Property="Foreground" Value="{StaticResource TextBrush}"/>
+      <Setter Property="FontWeight" Value="SemiBold"/>
+    </Style>
+  </UserControl.Styles>
+
+  <ItemsControl ItemsSource="{Binding #Root.Lines}">
+    <ItemsControl.ItemTemplate>
+      <DataTemplate x:DataType="vm:DiffLineViewModel">
+        <Border Classes="diff-line"
+                Tag="{Binding ClassName}"
+                Padding="4,1">
+          <Grid ColumnDefinitions="48,48,16,*">
+            <!-- Old line number -->
+            <TextBlock Grid.Column="0"
+                       Text="{Binding OldNo}"
+                       Classes="diff-lineno"
+                       HorizontalAlignment="Right"
+                       Margin="0,0,8,0"/>
+            <!-- New line number -->
+            <TextBlock Grid.Column="1"
+                       Text="{Binding NewNo}"
+                       Classes="diff-lineno"
+                       HorizontalAlignment="Right"
+                       Margin="0,0,8,0"/>
+            <!-- Sign -->
+            <TextBlock Grid.Column="2"
+                       Classes="diff-sign"
+                       Text="{Binding Sign}"
+                       FontFamily="{DynamicResource MonoFont}"
+                       FontSize="{StaticResource FontSizeMono}"/>
+            <!-- Line text -->
+            <TextBlock Grid.Column="3"
+                       Classes="diff-text"
+                       Text="{Binding Text}"
+                       FontFamily="{DynamicResource MonoFont}"
+                       FontSize="{StaticResource FontSizeMono}"
+                       TextWrapping="NoWrap"/>
+          </Grid>
+        </Border>
+      </DataTemplate>
+    </ItemsControl.ItemTemplate>
+  </ItemsControl>
+</UserControl>

src/ClaudeDo.Ui/Views/Controls/DiffLinesView.axaml.cs

@@ -0,0 +1,19 @@
+using System.Collections;
+using Avalonia;
+using Avalonia.Controls;
+
+namespace ClaudeDo.Ui.Views.Controls;
+
+public partial class DiffLinesView : UserControl
+{
+    public static readonly StyledProperty<IEnumerable?> LinesProperty =
+        AvaloniaProperty.Register<DiffLinesView, IEnumerable?>(nameof(Lines));
+
+    public IEnumerable? Lines
+    {
+        get => GetValue(LinesProperty);
+        set => SetValue(LinesProperty, value);
+    }
+
+    public DiffLinesView() => InitializeComponent();
+}

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

@@ -18,37 +18,6 @@
     <KeyBinding Gesture="Escape" Command="{Binding CloseCommand}"/>
   </Window.KeyBindings>
 
-  <Window.Styles>
-    <!-- diff line row tints via Tag selector (compiled-binding-friendly) -->
-    <Style Selector="Border.diff-line[Tag=add]">
-      <Setter Property="Background" Value="{StaticResource RunningTintBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=del]">
-      <Setter Property="Background" Value="{StaticResource ErrorTintBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=ctx]">
-      <Setter Property="Background" Value="Transparent"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-sign">
-      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-sign">
-      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-sign">
-      <Setter Property="Foreground" Value="{StaticResource TextFaintBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=add] TextBlock.diff-text">
-      <Setter Property="Foreground" Value="{StaticResource MossBrightBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=del] TextBlock.diff-text">
-      <Setter Property="Foreground" Value="{StaticResource BloodBrush}"/>
-    </Style>
-    <Style Selector="Border.diff-line[Tag=ctx] TextBlock.diff-text">
-      <Setter Property="Foreground" Value="{StaticResource TextDimBrush}"/>
-    </Style>
-  </Window.Styles>
-
   <ctl:ModalShell Title="{loc:Tr modals.diff.title}" CloseCommand="{Binding CloseCommand}">
     <ctl:ModalShell.Footer>
       <StackPanel Orientation="Horizontal" Spacing="8"
@@ -99,43 +68,7 @@
                    VerticalAlignment="Center"/>
         <ScrollViewer HorizontalScrollBarVisibility="Auto"
                     VerticalScrollBarVisibility="Auto">
-        <ItemsControl ItemsSource="{Binding SelectedFile.Lines}">
-          <ItemsControl.ItemTemplate>
-            <DataTemplate x:DataType="vm:DiffLineViewModel">
-              <Border Classes="diff-line"
-                      Tag="{Binding ClassName}"
-                      Padding="4,1">
-                <Grid ColumnDefinitions="48,48,16,*">
-                  <!-- Old line number -->
-                  <TextBlock Grid.Column="0"
-                             Text="{Binding OldNo}"
-                             Classes="diff-lineno"
-                             HorizontalAlignment="Right"
-                             Margin="0,0,8,0"/>
-                  <!-- New line number -->
-                  <TextBlock Grid.Column="1"
-                             Text="{Binding NewNo}"
-                             Classes="diff-lineno"
-                             HorizontalAlignment="Right"
-                             Margin="0,0,8,0"/>
-                  <!-- Sign -->
-                  <TextBlock Grid.Column="2"
-                             Classes="diff-sign"
-                             Text="{Binding Sign}"
-                             FontFamily="{DynamicResource MonoFont}"
-                             FontSize="{StaticResource FontSizeMono}"/>
-                  <!-- Line text -->
-                  <TextBlock Grid.Column="3"
-                             Classes="diff-text"
-                             Text="{Binding Text}"
-                             FontFamily="{DynamicResource MonoFont}"
-                             FontSize="{StaticResource FontSizeMono}"
-                             TextWrapping="NoWrap"/>
-                </Grid>
-              </Border>
-            </DataTemplate>
-          </ItemsControl.ItemTemplate>
-        </ItemsControl>
+          <ctl:DiffLinesView Lines="{Binding SelectedFile.Lines}"/>
         </ScrollViewer>
       </Grid>
     </Grid>

src/ClaudeDo.Ui/Views/Planning/PlanningDiffView.axaml

@@ -66,14 +66,7 @@
         <Grid Grid.Column="1" Background="{DynamicResource VoidBrush}">
           <ScrollViewer HorizontalScrollBarVisibility="Auto"
                         VerticalScrollBarVisibility="Auto">
-            <TextBox Text="{Binding DisplayedDiff, Mode=OneWay}"
-                     IsReadOnly="True"
-                     AcceptsReturn="True"
-                     FontFamily="{DynamicResource MonoFont}"
-                     FontSize="{StaticResource FontSizeBody}"
-                     Background="Transparent"
-                     BorderThickness="0"
-                     Padding="8"/>
+            <ctl:DiffLinesView Lines="{Binding DiffLines}"/>
           </ScrollViewer>
         </Grid>