fix(ui): surface resume-planning-session failures

ResumePlanningSessionAsync wrapped everything in an empty catch, so a
failed resume vanished silently. Report it via the footer error channel
with a dedicated planningResumeFailed message.

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

@@ -867,7 +867,7 @@ public sealed partial class TasksIslandViewModel : ViewModelBase, IDisposable
                     break;
             }
         }
-        catch { }
+        catch (Exception ex) { ErrorReported?.Invoke(Loc.T("vm.tasksIsland.planningResumeFailed", ex.Message)); }
     }
 
     [RelayCommand]