fix(merge): pass the stash consent to the conflict resolver so it opens on a dirty target

The resolver restarts the merge via StartConflictMerge, which had no autostash.
After a stash-retry approve reported 'conflict', the restart hit the same dirty
target, got 'dirty_target' and the resolver silently never opened. Thread the
consent through the hub, client, coordinator and resolver; surface a refusal in
the footer instead of dropping it.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/ClaudeDo.Ui/Services/MergeCoordinator.cs

@@ -14,8 +14,10 @@ namespace ClaudeDo.Ui.Services;
 public sealed class MergeCoordinator
 {
     /// Set once at composition to the shell's resolver entry. Null (headless/tests) ⇒ no-op.
-    public Func<string, string, Task>? Handler { get; set; }
+    public Func<string, string, bool, Task>? Handler { get; set; }
 
-    public Task ResolveConflictAsync(string taskId, string targetBranch) =>
-        Handler?.Invoke(taskId, targetBranch) ?? Task.CompletedTask;
+    /// <summary>Opens the resolver for <paramref name="taskId"/>; <paramref name="autostash"/> is the
+    /// caller's stash consent, repeated because the resolver restarts the merge on its own.</summary>
+    public Task ResolveConflictAsync(string taskId, string targetBranch, bool autostash = false) =>
+        Handler?.Invoke(taskId, targetBranch, autostash) ?? Task.CompletedTask;
 }