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>

PulseWidget/KeychainService.swift

@@ -0,0 +1,53 @@
+import Foundation
+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,
+            kSecAttrAccessGroup as String: accessGroup
+        ]
+        SecItemDelete(query as CFDictionary)
+        var add = query
+        add[kSecValueData as String] = data
+        add[kSecAttrAccessible as String] = kSecAttrAccessibleAfterFirstUnlock
+        SecItemAdd(add as CFDictionary, nil)
+    }
+
+    static func load(key: String) -> String? {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: service,
+            kSecAttrAccount as String: key,
+            kSecAttrAccessGroup as String: accessGroup,
+            kSecReturnData as String: true,
+            kSecMatchLimit as String: kSecMatchLimitOne
+        ]
+        var result: AnyObject?
+        guard SecItemCopyMatching(query as CFDictionary, &result) == errSecSuccess,
+              let data = result as? Data else { return nil }
+        return String(data: data, encoding: .utf8)
+    }
+
+    static func delete(key: String) {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: service,
+            kSecAttrAccount as String: key,
+            kSecAttrAccessGroup as String: accessGroup
+        ]
+        SecItemDelete(query as CFDictionary)
+    }
+
+    // Keys
+    static let tokenKey = "auth_token"
+    static let refreshTokenKey = "auth_refresh_token"
+    static let healthTokenKey = "health_jwt_token"
+    static let healthApiKeyKey = "health_api_key"
+}