feat(worker): add post-merge verification gate for list merges

Per-list optional VerifyCommand (list_config.verify_command) runs via
VerifyCommandRunner in the list's working dir right after a successful
merge/continue-merge, before the task is allowed to reach Done. A
non-zero exit or timeout leaves the merge in place but keeps the task
out of Done and reports StatusVerifyFailed with an output excerpt
through MergeResultDto/review_task; no command configured behaves
exactly as before. Merges against the same repo are now serialized
per working dir so a running verify can't be interrupted by a second
merge landing mid-build. Adds the field to the List Settings modal
(en/de localized) and covers success/failure/timeout in
TaskMergeServiceTests + VerifyCommandRunnerTests.

src/ClaudeDo.Ui/ViewModels/Agent/AgentConfigEditorViewModel.cs

@@ -184,7 +184,10 @@ public sealed partial class AgentConfigEditorViewModel : ViewModelBase, IDisposa
         catch { }
     }
 
-    public async System.Threading.Tasks.Task SaveAsync()
+    // verifyCommand is a List-only field owned by ListSettingsModalViewModel (not this editor,
+    // which is also reused for Task scope); the caller passes it through so the single
+    // UpdateListConfig call carries the full desired row instead of clobbering it.
+    public async System.Threading.Tasks.Task SaveAsync(string? verifyCommand = null)
     {
         if (TargetId is null) return;
         var model = string.IsNullOrWhiteSpace(Model) ? null : Model;
@@ -196,7 +199,7 @@ public sealed partial class AgentConfigEditorViewModel : ViewModelBase, IDisposa
         if (_scope == AgentConfigScope.Task)
             await _worker.UpdateTaskAgentSettingsAsync(new UpdateTaskAgentSettingsDto(TargetId, model, sp, ap, turns, skills));
         else
-            await _worker.UpdateListConfigAsync(new UpdateListConfigDto(TargetId, model, sp, ap, turns, skills));
+            await _worker.UpdateListConfigAsync(new UpdateListConfigDto(TargetId, model, sp, ap, turns, skills, verifyCommand));
     }
 
     private List<string>? SelectedSessionSkillNames()