feat(worker): surface rebase and worktree-maintenance progress on OperationProgress

RebaseOthersAfterMergeAsync now broadcasts a "rebasing" phase with i/n over the
WaitingForReview branches it checks, so the merge/continue_merge callers stop
showing the stalled "Merging…" phase while the best-effort rebase loop runs
(rebase still runs before the verify gate; a failed rebase still leaves the
merge itself successful). WorktreeMaintenanceService gained an optional
HubBroadcaster to report the same i/n shape per worktree during
cleanup/reset, with no new UI surface (deliberately out of scope). Both
review-action viewmodels now also listen on OperationProgressEvent (which
carries the total that the elapsed-seconds-only MergeProgressEvent drops) to
render "Rebasing other worktrees… (i/n)".

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

@@ -119,4 +119,26 @@ public class MergeModalViewModelTests
 
         Assert.Null(vm.ProgressMessage);
     }
+
+    [Fact]
+    public async Task Submit_shows_the_rebase_phase_with_branch_count_instead_of_stalled_merging()
+    {
+        var (vm, worker) = Build();
+        await vm.InitializeAsync("task-1", "do the thing");
+        worker.BlockMerge = true;
+
+        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.
+        worker.RaiseOperationProgress("task-1", "rebasing", 1, 2);
+        Assert.NotEqual(merging, vm.ProgressMessage);
+        Assert.Contains("(1/2)", vm.ProgressMessage);
+
+        worker.MergeGate.SetResult(new MergeResultDto("merged", new List<string>(), null));
+        await submit;
+
+        Assert.Null(vm.ProgressMessage);
+    }
 }