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)".

src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs

@@ -1290,7 +1290,15 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             if (progressTaskId != taskId || phase != MergePhaseVerifying) return;
             ApproveOp.Report(Loc.T("ops.merge.verifying", FormatElapsed(elapsedSeconds)));
         }
+        // Separate event: MergeProgressEvent forwards elapsed-seconds-only (verifying), but the
+        // rebase phase needs the branch count too, which only rides the untrimmed OperationProgress.
+        void OnOperationProgress(string opKey, string phase, int current, int total)
+        {
+            if (opKey != taskId || phase != MergePhaseRebasing) return;
+            ApproveOp.Report(FormatRebasing(current, total));
+        }
         _worker.MergeProgressEvent += OnMergeProgress;
+        _worker.OperationProgressEvent += OnOperationProgress;
         try
         {
             var hasChildren = Subtasks.Count > 0 || ChildOutcomes.Count > 0;
@@ -1314,15 +1322,24 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
         finally
         {
             _worker.MergeProgressEvent -= OnMergeProgress;
+            _worker.OperationProgressEvent -= OnOperationProgress;
         }
     }
 
     /// Mirrors TaskMergeService.PhaseVerifying — a hub payload token, not a display string.
     private const string MergePhaseVerifying = "verifying";
 
+    /// Mirrors TaskMergeService.PhaseRebasing — a hub payload token, not a display string.
+    private const string MergePhaseRebasing = "rebasing";
+
     private static string FormatElapsed(int seconds) =>
         TimeSpan.FromSeconds(Math.Max(0, seconds)).ToString(@"mm\:ss");
 
+    private static string FormatRebasing(int current, int total) =>
+        total > 0
+            ? $"{Loc.T("ops.worker.rebasingAfterMerge")} ({current}/{total})"
+            : Loc.T("ops.worker.rebasingAfterMerge");
+
     // Force the diff to have been opened before a merge can happen — but only when
     // there is actually something to inspect (a childless sandbox run with no worktree
     // has no diff, so it approves straight through).

src/ClaudeDo.Ui/ViewModels/Modals/MergeModalViewModel.cs

@@ -95,6 +95,7 @@ public sealed partial class MergeModalViewModel : ViewModelBase
         // client, and a transient VM left on that event would outlive its window.
         ProgressMessage = Loc.T("vm.merge.progressMerging");
         _worker.MergeProgressEvent += OnMergeProgress;
+        _worker.OperationProgressEvent += OnOperationProgress;
         try
         {
             var result = await _worker.MergeTaskAsync(
@@ -148,6 +149,7 @@ public sealed partial class MergeModalViewModel : ViewModelBase
         finally
         {
             _worker.MergeProgressEvent -= OnMergeProgress;
+            _worker.OperationProgressEvent -= OnOperationProgress;
             ProgressMessage = null;
             IsBusy = false;
         }
@@ -156,6 +158,9 @@ public sealed partial class MergeModalViewModel : ViewModelBase
     private void OnMergeProgress(string taskId, string phase, int elapsedSeconds)
     {
         if (taskId != TaskId) return;
+        // Rebasing is handled by OnOperationProgress (needs the branch total, which this
+        // elapsed-seconds-only forwarder drops) -- don't overwrite it with the generic fallback.
+        if (phase == MergePhaseRebasing) return;
         ProgressMessage = phase switch
         {
             MergePhaseVerifying => Loc.T("vm.merge.progressVerifying", FormatElapsed(elapsedSeconds)),
@@ -163,9 +168,22 @@ public sealed partial class MergeModalViewModel : ViewModelBase
         };
     }
 
+    // Separate event: MergeProgressEvent forwards elapsed-seconds-only (verifying), but the
+    // rebase phase needs the branch count too, which only rides the untrimmed OperationProgress.
+    private void OnOperationProgress(string opKey, string phase, int current, int total)
+    {
+        if (opKey != TaskId || phase != MergePhaseRebasing) return;
+        ProgressMessage = total > 0
+            ? $"{Loc.T("ops.worker.rebasingAfterMerge")} ({current}/{total})"
+            : Loc.T("ops.worker.rebasingAfterMerge");
+    }
+
     /// Mirrors TaskMergeService.PhaseVerifying — a hub payload token, not a display string.
     private const string MergePhaseVerifying = "verifying";
 
+    /// Mirrors TaskMergeService.PhaseRebasing — a hub payload token, not a display string.
+    private const string MergePhaseRebasing = "rebasing";
+
     private static string FormatElapsed(int seconds) =>
         TimeSpan.FromSeconds(Math.Max(0, seconds)).ToString(@"mm\:ss");