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>

tests/ClaudeDo.Ui.Tests/ViewModels/UnifiedDiffParserTests.cs

@@ -0,0 +1,109 @@
+using System.Linq;
+using ClaudeDo.Ui.ViewModels.Modals;
+
+namespace ClaudeDo.Ui.Tests.ViewModels;
+
+public class UnifiedDiffParserTests
+{
+    [Fact]
+    public void Modified_file_counts_additions_and_deletions()
+    {
+        const string raw =
+            "diff --git a/src/Foo.cs b/src/Foo.cs\n" +
+            "index 111..222 100644\n" +
+            "--- a/src/Foo.cs\n" +
+            "+++ b/src/Foo.cs\n" +
+            "@@ -1,3 +1,3 @@\n" +
+            " ctx\n" +
+            "-old\n" +
+            "+new\n";
+
+        var file = Assert.Single(UnifiedDiffParser.Parse(raw));
+        Assert.Equal("src/Foo.cs", file.Path);
+        Assert.Equal(DiffFileStatus.Modified, file.Status);
+        Assert.Equal("M", file.StatusCode);
+        Assert.Equal(1, file.Additions);
+        Assert.Equal(1, file.Deletions);
+        Assert.True(file.HasLines);
+        Assert.False(file.IsBinary);
+    }
+
+    [Fact]
+    public void New_file_is_marked_added()
+    {
+        const string raw =
+            "diff --git a/New.cs b/New.cs\n" +
+            "new file mode 100644\n" +
+            "index 000..abc\n" +
+            "--- /dev/null\n" +
+            "+++ b/New.cs\n" +
+            "@@ -0,0 +1,1 @@\n" +
+            "+hello\n";
+
+        var file = Assert.Single(UnifiedDiffParser.Parse(raw));
+        Assert.Equal(DiffFileStatus.Added, file.Status);
+        Assert.Equal("A", file.StatusCode);
+    }
+
+    [Fact]
+    public void Deleted_file_is_marked_deleted()
+    {
+        const string raw =
+            "diff --git a/Gone.cs b/Gone.cs\n" +
+            "deleted file mode 100644\n" +
+            "index abc..000\n" +
+            "--- a/Gone.cs\n" +
+            "+++ /dev/null\n" +
+            "@@ -1,1 +0,0 @@\n" +
+            "-bye\n";
+
+        var file = Assert.Single(UnifiedDiffParser.Parse(raw));
+        Assert.Equal(DiffFileStatus.Deleted, file.Status);
+        Assert.Equal("D", file.StatusCode);
+    }
+
+    [Fact]
+    public void Rename_captures_old_and_new_path()
+    {
+        const string raw =
+            "diff --git a/Old.cs b/New.cs\n" +
+            "similarity index 100%\n" +
+            "rename from Old.cs\n" +
+            "rename to New.cs\n";
+
+        var file = Assert.Single(UnifiedDiffParser.Parse(raw));
+        Assert.Equal(DiffFileStatus.Renamed, file.Status);
+        Assert.Equal("R", file.StatusCode);
+        Assert.Equal("Old.cs", file.OldPath);
+        Assert.Equal("New.cs", file.Path);
+    }
+
+    [Fact]
+    public void Binary_file_is_flagged_with_no_lines()
+    {
+        const string raw =
+            "diff --git a/img.png b/img.png\n" +
+            "new file mode 100644\n" +
+            "index 000..abc\n" +
+            "Binary files /dev/null and b/img.png differ\n";
+
+        var file = Assert.Single(UnifiedDiffParser.Parse(raw));
+        Assert.True(file.IsBinary);
+        Assert.False(file.HasLines);
+        Assert.False(file.IsEmptyContent);
+    }
+
+    [Fact]
+    public void Empty_new_file_reports_empty_content()
+    {
+        const string raw =
+            "diff --git a/Empty.txt b/Empty.txt\n" +
+            "new file mode 100644\n" +
+            "index 000..000\n";
+
+        var file = Assert.Single(UnifiedDiffParser.Parse(raw));
+        Assert.Equal(DiffFileStatus.Added, file.Status);
+        Assert.False(file.HasLines);
+        Assert.True(file.IsEmptyContent);
+    }
+}