chore(ui): remove IWorkerClient.MergeProgressEvent forwarder

Group C of the operation-feedback batch is fully merged; the two consumers
(DetailsIslandViewModel.ApproveReviewAsync, MergeModalViewModel) now handle
the verifying phase from the generic OperationProgressEvent handler instead
of a separate forwarder event.

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

@@ -79,7 +79,7 @@ public class MergeModalViewModelTests
 
         // The verify gate starts — a distinct phase, so the user sees why this is taking minutes.
         // (The elapsed time rides in a format argument, which the test localizer drops.)
-        worker.RaiseMergeProgress("task-1", "verifying", 90);
+        worker.RaiseOperationProgress("task-1", "verifying", 90, 0);
         Assert.NotEqual(merging, vm.ProgressMessage);
 
         worker.MergeGate.SetResult(new MergeResultDto("merged", new List<string>(), null));
@@ -100,7 +100,7 @@ public class MergeModalViewModelTests
         var submit = vm.SubmitCommand.ExecuteAsync(null);
         var merging = vm.ProgressMessage;
 
-        worker.RaiseMergeProgress("some-other-task", "verifying", 42);
+        worker.RaiseOperationProgress("some-other-task", "verifying", 42, 0);
 
         Assert.Equal(merging, vm.ProgressMessage);
 
@@ -115,7 +115,7 @@ public class MergeModalViewModelTests
         await vm.InitializeAsync("task-1", "do the thing");
 
         await vm.SubmitCommand.ExecuteAsync(null);
-        worker.RaiseMergeProgress("task-1", "verifying", 10);
+        worker.RaiseOperationProgress("task-1", "verifying", 10, 0);
 
         Assert.Null(vm.ProgressMessage);
     }
@@ -130,8 +130,7 @@ public class MergeModalViewModelTests
         var submit = vm.SubmitCommand.ExecuteAsync(null);
         var merging = vm.ProgressMessage;
 
-        // Needs the branch total, which only rides OperationProgress (MergeProgressEvent
-        // forwards elapsed-seconds only) -- and must not be clobbered by that other forwarder.
+        // Needs the branch total, which only OperationProgress carries.
         worker.RaiseOperationProgress("task-1", "rebasing", 1, 2);
         Assert.NotEqual(merging, vm.ProgressMessage);
         Assert.Contains("(1/2)", vm.ProgressMessage);