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/Islands/ListsIslandViewModel.cs

@@ -126,7 +126,11 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
         var dir = row?.WorkingDir;
         if (string.IsNullOrWhiteSpace(dir)) return;
         var findings = System.IO.Path.Combine(dir, ".claudedo");
-        if (!System.IO.Directory.Exists(findings)) return;
+        if (!System.IO.Directory.Exists(findings))
+        {
+            ErrorReported?.Invoke(Loc.T("vm.lists.findingsNotFound"));
+            return;
+        }
         try
         {
             System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo
@@ -135,7 +139,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
                 UseShellExecute = true,
             });
         }
-        catch { /* best-effort */ }
+        catch (Exception ex) { ErrorReported?.Invoke(Loc.T("vm.lists.findingsOpenFailed", ex.Message)); }
     }
 
     [RelayCommand]