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.Worker.Tests/Services/TaskMergeServiceTests.cs

@@ -1618,6 +1618,14 @@ public class TaskMergeServiceTests : IDisposable
         Assert.Equal(GitRepoFixture.RunGit(wtPathB, "rev-parse", "HEAD").Trim(), wtB.HeadCommit);
 
         Assert.Contains(proxy.Calls, c => c.Method == "WorktreeUpdated" && c.Args[0] is string s && s == taskB.Id);
+
+        // The rebase phase must be visible on the wire while it runs -- otherwise the UI still
+        // shows the stalled "Merging…" phase for the whole (best-effort) rebase loop.
+        Assert.Contains(proxy.Calls, c => c.Method == "OperationProgress"
+            && c.Args[0] is string opKey && opKey == taskA.Id
+            && c.Args[1] is string phase && phase == TaskMergeService.PhaseRebasing
+            && c.Args[2] is int current && current == 1
+            && c.Args[3] is int total && total == 1);
     }
 
     [Fact]