fix: widgets use App Group shared UserDefaults instead of Keychain

- Widgets can't access app's Keychain (different sandbox)
- App writes data to shared UserDefaults (group.com.daniil.pulsehealth)
- Widgets read from shared UserDefaults — no API calls needed
- WidgetDataService: updates widget data + reloads timelines
- DashboardView: pushes habits/tasks data to widget after load
- HealthView: pushes health data to widget after load
- App Group capability added to both app and widget entitlements
- Widgets update every 15 minutes from cached data

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

PulseHealth/Views/Dashboard/DashboardView.swift

@@ -203,6 +203,11 @@ struct DashboardView: View {
         }
         todayHabits = habits
         isLoading = false
+
+        // Update widget
+        let completed = habits.filter { $0.completedToday == true }.count
+        let activeTasks = todayTasks.filter { !$0.completed }.count
+        WidgetDataService.updateHabits(completed: completed, total: habits.count, tasksCount: activeTasks)
     }
 
     func filterHabitsForToday(_ habits: [Habit]) -> [Habit] {