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()

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

@@ -1073,6 +1073,10 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             var result = await _worker.ApproveReviewAsync(Task.Id, Merge.SelectedMergeTarget ?? "");
             if (!hasChildren && result?.Status == "conflict")
                 await _merge.ResolveConflictAsync(Task.Id, Merge.SelectedMergeTarget ?? "");
+            // The merge itself already landed; the verify command failed, so the task stayed
+            // out of Done. Surface that instead of silently looking like nothing happened.
+            else if (!hasChildren && result?.Status == "verify_failed" && ShowErrorAsync != null)
+                await ShowErrorAsync(result.ErrorMessage ?? Loc.T("vm.detailsIsland.verifyFailed"));
         }
         catch (Exception ex)
         {

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

@@ -30,6 +30,9 @@ public sealed partial class ListSettingsModalViewModel : ViewModelBase
     [ObservableProperty] private string _defaultCommitType = CommitTypeRegistry.DefaultType;
     // A manual list holds reminders: tasks created here start out manual (TaskEntity.IsManual).
     [ObservableProperty] private bool _isManual;
+    // Optional post-merge verification command (build/test), run in WorkingDir after a merge
+    // lands; a non-zero exit keeps the task out of Done instead of silently reporting merged.
+    [ObservableProperty] private string _verifyCommand = "";
 
     public ObservableCollection<string> CommitTypeOptions { get; } = new(CommitTypeRegistry.Types);
 
@@ -61,6 +64,8 @@ public sealed partial class ListSettingsModalViewModel : ViewModelBase
         DefaultCommitType = string.IsNullOrWhiteSpace(defaultCommitType) ? CommitTypeRegistry.DefaultType : defaultCommitType;
 
         await Agent.LoadForListAsync(listId, ct);
+        var cfg = await _worker.GetListConfigAsync(listId);
+        VerifyCommand = cfg?.VerifyCommand ?? "";
     }
 
     [RelayCommand]
@@ -73,7 +78,7 @@ public sealed partial class ListSettingsModalViewModel : ViewModelBase
             DefaultCommitType,
             IsManual));
 
-        await Agent.SaveAsync();
+        await Agent.SaveAsync(string.IsNullOrWhiteSpace(VerifyCommand) ? null : VerifyCommand);
 
         CloseAction?.Invoke();
     }