fix(ui): silent no-ops raise ErrorReported instead of swallowing failures (UX-Audit #1)

Stop/Enqueue/Dequeue/Reset&Retry (DetailsIslandViewModel), status/cancel/reject
commands (TasksIslandViewModel), Mission Control's drag-enqueue and queue
refresh, and "Open findings folder" (ListsIslandViewModel) used to catch {}
or silently return on a blocked precondition. They now report through the
existing ErrorReported -> FlashFooterError path, with new en/de locale keys
and Ui.Tests covering each converted command.

src/ClaudeDo.Ui/ViewModels/MissionControlViewModel.cs

@@ -119,7 +119,7 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
             }
             OnPropertyChanged(nameof(HasQueued));
         }
-        catch { /* best-effort queue refresh */ }
+        catch (Exception ex) { ErrorReported?.Invoke(Loc.T("missionControl.queueRefreshFailed", ex.Message)); }
     }
 
     // Drop-to-queue: a task dragged from the main app onto Mission Control gets queued. Goes
@@ -130,7 +130,11 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
     public async System.Threading.Tasks.Task EnqueueTaskAsync(string taskId)
     {
         if (string.IsNullOrEmpty(taskId)) return;
-        if (ConPtySessions.Any(s => s.TaskId == taskId)) return;
+        if (ConPtySessions.Any(s => s.TaskId == taskId))
+        {
+            ErrorReported?.Invoke(Loc.T("missionControl.enqueueAlreadyOpen"));
+            return;
+        }
         try
         {
             var baseDirty = await _worker.SetTaskStatusAsync(taskId, ClaudeDo.Data.Models.TaskStatus.Queued);
@@ -138,7 +142,7 @@ public sealed partial class MissionControlViewModel : ViewModelBase, IDisposable
                 ErrorReported?.Invoke(Loc.T(
                     "vm.queue.baseDirtyWarning", baseDirty.ModifiedCount, baseDirty.UntrackedCount));
         }
-        catch { /* best-effort enqueue */ }
+        catch (Exception ex) { ErrorReported?.Invoke(Loc.T("missionControl.enqueueFailed", ex.Message)); }
         await RefreshQueueAsync();
     }