feat(daily-prep): trigger planning from inside the prep-log window with an empty-state hint

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -346,6 +346,8 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase
             RecomputeCanMergeAll();
             ReviewCombinedDiffCommand.NotifyCanExecuteChanged();
         };
+
+        PrepLog.CollectionChanged += (_, _) => OnPropertyChanged(nameof(ShowPrepEmptyState));
     }
 
     private void OnTaskMessage(string taskId, string line)
@@ -381,6 +383,18 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase
         AppendClaudeText(formatted, target, buf);
     }
 
+    [RelayCommand]
+    private async Task PlanDayAsync()
+    {
+        if (_worker is null) return;
+        try { await _worker.RunDailyPrepNowAsync(); }
+        catch { /* worker offline; PrepStarted/PrepLine will reconcile */ }
+    }
+
+    public bool ShowPrepEmptyState => !IsPrepRunning && PrepLog.Count == 0;
+
+    partial void OnIsPrepRunningChanged(bool value) => OnPropertyChanged(nameof(ShowPrepEmptyState));
+
     private void OnPrepStarted()
     {
         PrepLog.Clear();