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/ViewModels/IslandsShellViewModel.cs

@@ -154,21 +154,23 @@ public sealed partial class IslandsShellViewModel : ViewModelBase, IDisposable
         if (ShowConflictDialog == null || _dbFactory == null) return;
 
         string subtaskTitle = subtaskId;
-        string worktreePath = System.Environment.CurrentDirectory;
+        // The conflict lives in the list's working dir (the repo being merged into),
+        // not the subtask worktree. VS Code must open this folder to show the merge UI.
+        string repoDirectory = System.Environment.CurrentDirectory;
         string targetBranch = Worker?.LastApproveTarget ?? "main";
 
         try
         {
             await using var ctx = await _dbFactory.CreateDbContextAsync();
             var entity = await ctx.Tasks
-                .Include(t => t.Worktree)
+                .Include(t => t.List)
                 .AsNoTracking()
                 .FirstOrDefaultAsync(t => t.Id == subtaskId);
             if (entity != null)
             {
                 subtaskTitle = entity.Title;
-                if (entity.Worktree?.Path is { } p)
-                    worktreePath = p;
+                if (entity.List?.WorkingDir is { } dir && !string.IsNullOrWhiteSpace(dir))
+                    repoDirectory = dir;
             }
         }
         catch { /* Non-fatal: fall back to subtaskId and cwd */ }
@@ -179,7 +181,7 @@ public sealed partial class IslandsShellViewModel : ViewModelBase, IDisposable
             subtaskTitle,
             targetBranch,
             conflictedFiles,
-            worktreePath);
+            repoDirectory);
 
         await ShowConflictDialog(vm);
     }