feat: iOS widgets + fix sleep showing yesterday's data

Widgets:
- HabitsProgressWidget (small/medium): progress ring, completed/total habits, tasks count
- HealthSummaryWidget (small/medium): readiness score, steps, sleep, heart rate
- Shared Keychain access group for app ↔ widget token sharing
- Widget data refreshes every 30 minutes

Sleep fix:
- Changed sleep window from "24 hours back" to "6 PM yesterday → now"
- Captures overnight sleep correctly without showing previous day's data
- Applied to both fetchSleepData (sync) and fetchSleepSegments (detail view)

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

PulseHealth/Services/KeychainService.swift

@@ -3,13 +3,15 @@ import Security
 
 enum KeychainService {
     static let service = "com.daniil.pulsehealth"
+    static let accessGroup = "V9AG8JTFLC.com.daniil.pulsehealth.shared"
 
     static func save(key: String, value: String) {
         guard let data = value.data(using: .utf8) else { return }
         let query: [String: Any] = [
             kSecClass as String: kSecClassGenericPassword,
             kSecAttrService as String: service,
-            kSecAttrAccount as String: key
+            kSecAttrAccount as String: key,
+            kSecAttrAccessGroup as String: accessGroup
         ]
         SecItemDelete(query as CFDictionary)
         var add = query
@@ -23,6 +25,7 @@ enum KeychainService {
             kSecClass as String: kSecClassGenericPassword,
             kSecAttrService as String: service,
             kSecAttrAccount as String: key,
+            kSecAttrAccessGroup as String: accessGroup,
             kSecReturnData as String: true,
             kSecMatchLimit as String: kSecMatchLimitOne
         ]
@@ -36,7 +39,8 @@ enum KeychainService {
         let query: [String: Any] = [
             kSecClass as String: kSecClassGenericPassword,
             kSecAttrService as String: service,
-            kSecAttrAccount as String: key
+            kSecAttrAccount as String: key,
+            kSecAttrAccessGroup as String: accessGroup
         ]
         SecItemDelete(query as CFDictionary)
     }