fix(ui): clearer rename display in diff viewer

Show renames as old → new in the file header and suppress the misleading
"+0 −0" stats for a pure rename (the R badge already conveys it).

src/ClaudeDo.Ui/ViewModels/Modals/DiffModels.cs

@@ -54,6 +54,14 @@ public sealed class DiffFileViewModel
 
     /// A text file that produced no diff hunks (e.g. a newly added empty file).
     public bool IsEmptyContent => !IsBinary && Lines.Count == 0;
+
+    /// A rename with no content change — showing "+0 −0" for it is misleading.
+    public bool IsPureRename => Status == DiffFileStatus.Renamed && Additions == 0 && Deletions == 0;
+
+    /// Header path label: for a rename, spell out old → new; otherwise just the path.
+    public string HeaderPath => Status == DiffFileStatus.Renamed && !string.IsNullOrEmpty(OldPath)
+        ? $"{OldPath} → {Path}"
+        : Path;
 }
 
 /// One row in the planning subtask list (left pane in Planning mode).
@@ -72,7 +80,7 @@ public sealed partial class DiffTreeNodeViewModel : ViewModelBase
     [ObservableProperty] private bool _isExpanded = true;
 
     public string? StatusCode => File?.StatusCode;
-    public bool ShowStats => File is { IsBinary: false };
+    public bool ShowStats => File is { IsBinary: false, IsPureRename: false };
     public int Additions => File?.Additions ?? 0;
     public int Deletions => File?.Deletions ?? 0;
 }

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

@@ -131,7 +131,7 @@
                                FontFamily="{DynamicResource MonoFont}" FontSize="{StaticResource FontSizeEyebrow}"
                                Foreground="{DynamicResource TextBrush}"/>
                   </Border>
-                  <TextBlock Grid.Column="1" Classes="path-mono" Text="{Binding SelectedFile.Path}"
+                  <TextBlock Grid.Column="1" Classes="path-mono" Text="{Binding SelectedFile.HeaderPath}"
                              VerticalAlignment="Center" TextTrimming="PrefixCharacterEllipsis"/>
                 </Grid>
               </Border>