fix(worker-client): stop swallowing mutating hub call failures

TryInvokeAsync catches every exception and returns null, which is fine
for read-only calls but hid real HubException reasons behind a generic
"offline" message for the 7 mutating call sites (RestoreDefaultAgents,
UpsertPrimeSchedule, AddDailyNote, CleanupFinishedWorktrees,
ResetAllWorktrees, ForceRemoveWorktree, BuildPlanningIntegrationBranch)
— the same bug class fixed for ApproveReview in e1807fd. Each of the 22
TryInvokeAsync call sites was audited; the 15 read-only ones are left
unchanged (empty/offline is the right display). For the 7 switched to
a direct hub invoke, every caller was checked and, where it had no
catch, one was added so the exception surfaces (StatusMessage,
ShowErrorAsync/CombinedWarning) instead of crashing.

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

@@ -197,6 +197,11 @@ public sealed partial class DiffViewerViewModel : ViewModelBase
                     DisplayedDiff = "";
                 }
             }
+            catch (Exception ex)
+            {
+                DisplayedDiff = "";
+                CombinedWarning = Loc.T("vm.planningDiff.buildFailed", ex.Message);
+            }
             finally
             {
                 IsLoadingCombined = false;