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>

tests/ClaudeDo.Ui.Tests/ViewModels/WorktreesOverviewBatchMergeTests.cs

@@ -141,7 +141,7 @@ public class WorktreesOverviewBatchMergeTests
         (string Task, string Target)? captured = null;
         var coordinator = new ClaudeDo.Ui.Services.MergeCoordinator
         {
-            Handler = (taskId, target) => { captured = (taskId, target); return System.Threading.Tasks.Task.CompletedTask; },
+            Handler = (taskId, target, _) => { captured = (taskId, target); return System.Threading.Tasks.Task.CompletedTask; },
         };
         var vm = NewVm(coordinator);
         vm.SelectedTarget = "release";