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.Worker/Planning/PlanningMergeOrchestrator.cs

@@ -199,6 +199,10 @@ public sealed class PlanningMergeOrchestrator
         parent.FinishedAt = DateTime.UtcNow;
         await ctx.SaveChangesAsync(ct);
 
+        // Surface the Done transition to the UI. Without this the parent row stays
+        // visibly stuck in WaitingForReview even though the unit merge completed.
+        await _broadcaster.TaskUpdated(parentTaskId);
+
         // Only planning builds an integration branch via the aggregator; skip cleanup otherwise.
         if (isPlanning)
         {