FRE-4738: Implement mark-as-read and mark-all-read actions

- Extract NotificationItem/NotificationType to Models/Notification.swift
- Create NotificationsServiceProtocol with testable service layer
- Implement markAsRead(id:) and markAllAsRead() with HTTP calls
- Add NotificationError enum with localized descriptions
- Update NotificationsViewModel to use protocol-based service
- Add 18 unit tests (12 ViewModel + 6 Model) with mock service
- Update README with architecture documentation

Lendair/Models/Notification.swift

@@ -0,0 +1,92 @@
+import Foundation
+import SwiftUI
+
+// MARK: - Notification Item
+
+struct NotificationItem: Identifiable, Equatable, Codable {
+    let id: String
+    let type: NotificationType
+    let title: String
+    let message: String
+    let createdAt: Date
+    var isRead: Bool
+
+    enum CodingKeys: String, CodingKey {
+        case id, type, title, message, createdAt, isRead
+    }
+
+    init(id: String, type: NotificationType, title: String, message: String, createdAt: Date, isRead: Bool) {
+        self.id = id
+        self.type = type
+        self.title = title
+        self.message = message
+        self.createdAt = createdAt
+        self.isRead = isRead
+    }
+
+    static func == (lhs: NotificationItem, rhs: NotificationItem) -> Bool {
+        lhs.id == rhs.id && lhs.isRead == rhs.isRead
+    }
+}
+
+// MARK: - Notification Type
+
+enum NotificationType: String, CaseIterable, Codable {
+    case loanApproved = "LOAN_APPROVED"
+    case loanRejected = "LOAN_REJECTED"
+    case paymentReceived = "PAYMENT_RECEIVED"
+    case paymentDue = "PAYMENT_DUE"
+    case newLender = "NEW_LENDER"
+    case systemUpdate = "SYSTEM_UPDATE"
+
+    var icon: String {
+        switch self {
+        case .loanApproved: return "checkmark.circle.fill"
+        case .loanRejected: return "xmark.circle.fill"
+        case .paymentReceived: return "arrow.down.circle.fill"
+        case .paymentDue: return "exclamationmark.circle.fill"
+        case .newLender: return "person.circle.fill"
+        case .systemUpdate: return "info.circle.fill"
+        }
+    }
+
+    var color: Color {
+        switch self {
+        case .loanApproved: return .green
+        case .loanRejected: return .red
+        case .paymentReceived: return .green
+        case .paymentDue: return .orange
+        case .newLender: return .blue
+        case .systemUpdate: return .gray
+        }
+    }
+}
+
+// MARK: - List Parameters
+
+struct NotificationListParams: Encodable {
+    var limit: Int
+    var offset: Int
+
+    init(limit: Int = 20, offset: Int = 0) {
+        self.limit = limit
+        self.offset = offset
+    }
+}
+
+// MARK: - API Response Types
+
+struct NotificationListResponse: Decodable {
+    let notifications: [NotificationItem]
+    let hasMore: Bool
+}
+
+struct NotificationMarkAsReadResponse: Decodable {
+    let success: Bool
+    let notificationId: String
+}
+
+struct NotificationMarkAllReadResponse: Decodable {
+    let success: Bool
+    let markedCount: Int
+}