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/PulseHealth.entitlements

@@ -6,9 +6,9 @@
 	<true/>
 	<key>com.apple.developer.healthkit.background-delivery</key>
 	<true/>
-	<key>keychain-access-groups</key>
+	<key>com.apple.security.application-groups</key>
 	<array>
-		<string>$(AppIdentifierPrefix)com.daniil.pulsehealth.shared</string>
+		<string>group.com.daniil.pulsehealth</string>
 	</array>
 </dict>
 </plist>