feat: add complete Mayday iOS Xcode project

- Swift 6, SwiftUI, MVVM + async/await architecture
- iOS 17.0 minimum deployment target
- Two targets: Mayday app + MaydayLiveActivity widget extension
- Models: UserResponse, TokenPair, AppNotification, SessionResponse, AlertAttributes
- Services: HTTPClient (actor), AuthService, KeychainService, NotificationsAPIService, PushNotificationService
- ViewModels: AuthViewModel, NotificationsViewModel, SettingsViewModel
- Views: Login/Register/VerifyEmail, NotificationsList/Detail, Settings/ChangePassword/Sessions
- APNs push notifications with UIApplicationDelegate
- ActivityKit Live Activities for Dynamic Island + Lock Screen
- Keychain (Security framework) token storage
- 30-second polling with pagination for notifications
- Xcode project file (project.pbxproj) with correct build phases for both targets

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Mayday/Services/KeychainService.swift

@@ -0,0 +1,74 @@
+import Foundation
+import Security
+
+final class KeychainService: Sendable {
+    static let shared = KeychainService()
+    
+    private let accessTokenKey = "mayday.access_token"
+    private let refreshTokenKey = "mayday.refresh_token"
+    private let expiresAtKey = "mayday.expires_at"
+
+    private init() {}
+
+    func saveTokens(_ tokens: TokenPair) throws {
+        try save(tokens.accessToken, forKey: accessTokenKey)
+        try save(tokens.refreshToken, forKey: refreshTokenKey)
+        let expiresAtString = ISO8601DateFormatter().string(from: tokens.expiresAt)
+        try save(expiresAtString, forKey: expiresAtKey)
+    }
+
+    func loadAccessToken() -> String? {
+        load(forKey: accessTokenKey)
+    }
+
+    func loadRefreshToken() -> String? {
+        load(forKey: refreshTokenKey)
+    }
+
+    func clearTokens() {
+        delete(forKey: accessTokenKey)
+        delete(forKey: refreshTokenKey)
+        delete(forKey: expiresAtKey)
+    }
+
+    private func save(_ value: String, forKey key: String) throws {
+        let data = Data(value.utf8)
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrAccount as String: key,
+            kSecValueData as String: data
+        ]
+        SecItemDelete(query as CFDictionary)
+        let status = SecItemAdd(query as CFDictionary, nil)
+        guard status == errSecSuccess else {
+            throw KeychainError.saveFailed(status)
+        }
+    }
+
+    private func load(forKey key: String) -> String? {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrAccount as String: key,
+            kSecReturnData as String: true,
+            kSecMatchLimit as String: kSecMatchLimitOne
+        ]
+        var result: AnyObject?
+        let status = SecItemCopyMatching(query as CFDictionary, &result)
+        guard status == errSecSuccess,
+              let data = result as? Data,
+              let string = String(data: data, encoding: .utf8) else { return nil }
+        return string
+    }
+
+    private func delete(forKey key: String) {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrAccount as String: key
+        ]
+        SecItemDelete(query as CFDictionary)
+    }
+}
+
+enum KeychainError: Error {
+    case saveFailed(OSStatus)
+}