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/Services/WidgetDataService.swift

@@ -0,0 +1,25 @@
+import Foundation
+import WidgetKit
+
+enum WidgetDataService {
+    static let suiteName = "group.com.daniil.pulsehealth"
+
+    static var shared: UserDefaults? {
+        UserDefaults(suiteName: suiteName)
+    }
+
+    static func updateHabits(completed: Int, total: Int, tasksCount: Int) {
+        shared?.set(completed, forKey: "w_habits_completed")
+        shared?.set(total, forKey: "w_habits_total")
+        shared?.set(tasksCount, forKey: "w_tasks_count")
+        WidgetCenter.shared.reloadTimelines(ofKind: "HabitsProgress")
+    }
+
+    static func updateHealth(steps: Int, sleep: Double, heartRate: Int, readiness: Int) {
+        shared?.set(steps, forKey: "w_steps")
+        shared?.set(sleep, forKey: "w_sleep")
+        shared?.set(heartRate, forKey: "w_heart_rate")
+        shared?.set(readiness, forKey: "w_readiness")
+        WidgetCenter.shared.reloadTimelines(ofKind: "HealthSummary")
+    }
+}