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/ConflictResolutionViewModelTests.cs

@@ -36,7 +36,7 @@ public class ConflictResolutionViewModelTests
             subtaskTitle: "My subtask",
             targetBranch: "main",
             conflictedFiles: new[] { "src/Foo.cs", "src/Bar.cs" },
-            worktreePath: "C:/worktrees/plan-1");
+            repoDirectory: "C:/repos/plan-1");
 
     // ------------------------------------------------------------------ tests