Initial project

apps/im_app/lib/features/app_tab/view/app_tab.dart

@@ -0,0 +1,52 @@
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+
+/// 主 Tab 容器（Shell 层）
+///
+/// 由 [StatefulShellRoute.indexedStack] 驱动，不持有任何状态。
+/// Tab 切换通过 [navigationShell.goBranch] 完成，go_router 负责保持各 Tab 的导航栈。
+///
+/// Tabs（index 顺序）：
+/// - 0：聊天
+/// - 1：联系人
+/// - 2：设置
+class AppTab extends StatelessWidget {
+  const AppTab({
+    super.key,
+    required this.navigationShell,
+  });
+
+  final StatefulNavigationShell navigationShell;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: navigationShell,
+      bottomNavigationBar: BottomNavigationBar(
+        currentIndex: navigationShell.currentIndex,
+        onTap: (index) => navigationShell.goBranch(
+          index,
+          // 再次点击已激活的 Tab 时回到该 Tab 的初始路由
+          initialLocation: index == navigationShell.currentIndex,
+        ),
+        items: const [
+          BottomNavigationBarItem(
+            icon: Icon(Icons.chat_bubble_outline),
+            activeIcon: Icon(Icons.chat_bubble),
+            label: '聊天',
+          ),
+          BottomNavigationBarItem(
+            icon: Icon(Icons.people_outline),
+            activeIcon: Icon(Icons.people),
+            label: '联系人',
+          ),
+          BottomNavigationBarItem(
+            icon: Icon(Icons.settings_outlined),
+            activeIcon: Icon(Icons.settings),
+            label: '设置',
+          ),
+        ],
+      ),
+    );
+  }
+}