Add login flow, session routing, and MainTab shell aligned with reference UI.

Implement token-based root routing, Android-matched login screen, five-slot MainTabBar with scan action, and placeholder tab pages.

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkan/UI/MainTab/TabNavigationController.swift

@@ -0,0 +1,73 @@
+//
+//  TabNavigationController.swift
+//  suixinkan
+//
+
+import UIKit
+
+/// 单个 Tab 的导航栈。
+final class TabNavigationController: UINavigationController {
+
+    let appTab: AppTab
+
+    init(tab: AppTab) {
+        self.appTab = tab
+        super.init(nibName: nil, bundle: nil)
+        delegate = self
+        navigationBar.prefersLargeTitles = false
+        setViewControllers([tab.makeRootViewController()], animated: false)
+    }
+
+    @available(*, unavailable)
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    override func pushViewController(_ viewController: UIViewController, animated: Bool) {
+        viewController.hidesBottomBarWhenPushed = viewControllers.count > 0
+        updateNavigationBarVisibility(for: viewController, animated: animated)
+        super.pushViewController(viewController, animated: animated)
+    }
+
+    override func setViewControllers(_ viewControllers: [UIViewController], animated: Bool) {
+        if let topViewController = viewControllers.last {
+            updateNavigationBarVisibility(for: topViewController, animated: animated)
+        }
+        super.setViewControllers(viewControllers, animated: animated)
+    }
+
+    override func popViewController(animated: Bool) -> UIViewController? {
+        let poppedViewController = super.popViewController(animated: animated)
+        if !animated, let topViewController {
+            updateNavigationBarVisibility(for: topViewController, animated: false)
+        }
+        return poppedViewController
+    }
+
+    override func popToRootViewController(animated: Bool) -> [UIViewController]? {
+        let poppedViewControllers = super.popToRootViewController(animated: animated)
+        if !animated, let topViewController {
+            updateNavigationBarVisibility(for: topViewController, animated: false)
+        }
+        return poppedViewControllers
+    }
+
+    private func shouldHideNavigationBar(for viewController: UIViewController) -> Bool {
+        viewController is HomeViewController
+    }
+
+    private func updateNavigationBarVisibility(for viewController: UIViewController, animated: Bool) {
+        setNavigationBarHidden(shouldHideNavigationBar(for: viewController), animated: animated)
+    }
+}
+
+extension TabNavigationController: UINavigationControllerDelegate {
+
+    func navigationController(
+        _ navigationController: UINavigationController,
+        willShow viewController: UIViewController,
+        animated: Bool
+    ) {
+        updateNavigationBarVisibility(for: viewController, animated: animated)
+    }
+}