feat(ios): tab tabanlı navigasyon ve okuma durumu takibi ekle

ios/Bookibra/App/AppRouter.swift

@@ -3,17 +3,25 @@ import SwiftUI
 
 @MainActor
 final class AppRouter: ObservableObject {
+    enum Tab: Hashable {
+        case library
+        case discover
+        case stats
+        case profile
+    }
+
     enum Route: Hashable {
-        case addBooks
         case category(name: String)
         case detail(BookRemote)
     }
 
     @Published var isAuthenticated = false
+    @Published var selectedTab: Tab = .library
     @Published var path: [Route] = []
 
     func resetToHome() {
         path.removeAll()
+        selectedTab = .library
     }
 }