feat(mission-control): give the list handler its own review task

"Let Claude handle it" now creates one ClaudeDo task per run to host the
ConPTY session (Idle/IsManual, never queued) instead of an untracked
ad-hoc tile, so the run has a real title, diff, and review outcome.
Since the handler merges its own changes straight into the list's
working dir, the task never gets a WorktreeEntity; its review range
lives as new HandlerBaseCommit/HandlerHeadCommit columns on TaskEntity
instead, reusing the existing commit-range diff machinery and keeping
it out of the worktrees overview entirely.

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

@@ -42,8 +42,11 @@ public sealed partial class MergeSectionViewModel : ViewModelBase
     public bool ShowMergePreviewMuted =>
         !MergeIsClean && !MergeIsConflict && !string.IsNullOrEmpty(MergePreviewText);
 
+    // CanDiffMergedRange covers a worktree-less list-handler host task (no live worktree, but
+    // a HandlerBaseCommit/HandlerHeadCommit review range over the list's working dir) so its
+    // merge/diff card still renders even though _worktreePath stays null for it.
     public bool ShowMergeSection =>
-        _worktreePath != null || _isPlanningParent || _hasChildOutcomes;
+        _worktreePath != null || _isPlanningParent || _hasChildOutcomes || CanDiffMergedRange;
 
     public Func<DiffViewerViewModel, System.Threading.Tasks.Task>? ShowDiffViewer { get; set; }
     public Func<MergeModalViewModel, System.Threading.Tasks.Task>? ShowMergeModal { get; set; }