feat(ui): richer diff viewer + surface child roadblocks on parents

- UnifiedDiffParser detects added/deleted/renamed/binary files; diff
  modal shows a file list, binary/empty placeholders, and can diff a
  merged task by commit range after its worktree is gone
- DetailsIslandViewModel flags children needing attention (failed,
  cancelled, awaiting review, or with roadblocks) on the parent
- GitService gains worktree head-commit/range support; planning chain,
  merge orchestration, and session manager tweaks with updated tests
- refresh app/installer/worker icons

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Ui/Views/Islands/Detail/WorkConsole.axaml

@@ -313,6 +313,22 @@
         <ScrollViewer IsVisible="{Binding IsSessionTab}" Padding="14,10">
           <StackPanel Spacing="14">
 
+            <!-- Attention band: a child failed, was cancelled, still needs its own
+                 review, or reported roadblocks. The parent stays waiting until resolved. -->
+            <Border IsVisible="{Binding HasChildrenNeedingAttention}"
+                    Background="{DynamicResource ErrorTintBrush}"
+                    BorderBrush="{DynamicResource BloodBrush}"
+                    BorderThickness="1" CornerRadius="8" Padding="10,8">
+              <StackPanel Orientation="Horizontal" Spacing="8">
+                <PathIcon Data="{StaticResource Icon.Warning}"
+                          Foreground="{DynamicResource BloodBrush}"
+                          Width="14" Height="14" VerticalAlignment="Center" />
+                <TextBlock Classes="meta" Text="{Binding ChildrenAttentionText}"
+                           Foreground="{DynamicResource BloodBrush}"
+                           VerticalAlignment="Center" />
+              </StackPanel>
+            </Border>
+
             <!-- Child outcomes -->
             <StackPanel Spacing="6" IsVisible="{Binding HasChildOutcomes}">
               <TextBlock Classes="section-label" Text="OUTCOMES" />