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/PlanningMcpService.cs

@@ -135,7 +135,7 @@ public sealed class PlanningMcpService
         await BroadcastTaskUpdatedAsync(ctx.ParentTaskId, cancellationToken);
     }
 
-    [McpServerTool, Description("Finalize the planning session, promoting all draft child tasks to queued or manual status.")]
+    [McpServerTool, Description("Finalize the planning session. Child tasks are left idle and chain-linked (each blocked by its predecessor); they are NOT queued automatically — the user queues the plan from the app when ready. The queueAgentTasks argument is accepted for compatibility but ignored.")]
     public async Task<int> Finalize(
         bool queueAgentTasks,
         CancellationToken cancellationToken)
@@ -149,8 +149,10 @@ public sealed class PlanningMcpService
 
         var children = await _tasks.GetChildrenAsync(ctx.ParentTaskId, cancellationToken);
         int count = children.Count;
-        if (queueAgentTasks && children.Count > 0)
-            count = await _chain.SetupChainAsync(ctx.ParentTaskId, cancellationToken);
+        // Establish the blocked-by chain but leave children Idle; queueing is a
+        // deliberate user action ("Queue plan"), never an automatic finalize step.
+        if (children.Count > 0)
+            count = await _chain.SetupChainAsync(ctx.ParentTaskId, enqueue: false, cancellationToken);
 
         foreach (var c in children)
             await BroadcastTaskUpdatedAsync(c.Id, cancellationToken);