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/IslandsShellViewModelExternalMergeTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Threading.Tasks;
 using ClaudeDo.Data.Models;
+using ClaudeDo.Ui.Services;
 using ClaudeDo.Ui.ViewModels;
 using Xunit;
 
@@ -124,4 +125,26 @@ public class IslandsShellViewModelExternalMergeTests
         // click must degrade gracefully rather than throw, same as the existing UI-driven path.
         await vm.OpenExternalMergeConflictCommand.ExecuteAsync(null);
     }
+
+    private sealed class DirtyTargetWorker : StubWorkerClient
+    {
+        public override Task<MergeResultDto> StartConflictMergeAsync(string taskId, string targetBranch, bool autostash = false) =>
+            Task.FromResult(new MergeResultDto("dirty_target", Array.Empty<string>(), "target working tree has uncommitted changes"));
+    }
+
+    [Fact]
+    public async Task RequestConflictResolution_ResolverRefused_ShowsWhyInTheFooter()
+    {
+        // Regression: a refusal (dirty target, ...) left the resolver closed with no explanation anywhere.
+        var vm = new IslandsShellViewModel
+        {
+            Dialogs = new RecordingDialogService(),
+            ConflictResolverFactory = id => new ClaudeDo.Ui.ViewModels.Conflicts.ConflictResolverViewModel(new DirtyTargetWorker(), id),
+        };
+
+        await vm.RequestConflictResolutionAsync("t1", "main");
+
+        Assert.Equal(WorkerLogLevel.Error, vm.WorkerLogLevel);
+        Assert.Contains("uncommitted changes", vm.WorkerLogText);
+    }
 }