feat(mobile,account-service): 统一发送服务 + 员工目录接口 + 好友申请五态/验证消息（B-52 施工 2/3）

- message_send_service：所有消息走统一门禁（登录/连接/空接收方/好友校验），
  失败打印 SDK 原始 code 并映射中文提示，不再只吞异常
- chat_screen 接入统一发送服务，失败提示真实原因
- account-service 新增 GET /api/directory（登录用户可读启用员工，用于添加同事）
- add_friend_screen 增加可编辑验证消息（视觉规范 4.2）
- new_friends_screen 五态 + 窄屏(<360)按钮组换行不挤压姓名（视觉规范 5.3）

Co-authored-by: multica-agent <github@multica.ai>

mobile/lib/screens/add_friend_screen.dart

@@ -3,7 +3,7 @@ import 'package:flutter_openim_sdk/flutter_openim_sdk.dart';
 
 import '../theme.dart';
 
-/// 添加同事：输入对方工号（userID）发送好友申请
+/// 添加同事：输入对方工号（userID）+ 可编辑验证消息，发送好友申请
 class AddFriendScreen extends StatefulWidget {
   const AddFriendScreen({super.key});
 
@@ -13,11 +13,13 @@ class AddFriendScreen extends StatefulWidget {
 
 class _AddFriendScreenState extends State<AddFriendScreen> {
   final TextEditingController _idCtrl = TextEditingController();
+  final TextEditingController _msgCtrl = TextEditingController(text: '你好，我想加你为同事');
   bool _sending = false;
 
   @override
   void dispose() {
     _idCtrl.dispose();
+    _msgCtrl.dispose();
     super.dispose();
   }
 
@@ -29,7 +31,7 @@ class _AddFriendScreenState extends State<AddFriendScreen> {
     }
     setState(() => _sending = true);
     try {
-      await OpenIM.iMManager.friendshipManager.addFriend(userID: userID, reason: '你好，我想加你为同事');
+      await OpenIM.iMManager.friendshipManager.addFriend(userID: userID, reason: _msgCtrl.text.trim());
       if (!mounted) return;
       _toast('申请已发送，等对方通过');
       Navigator.of(context).pop();
@@ -66,6 +68,22 @@ class _AddFriendScreenState extends State<AddFriendScreen> {
                 ),
               ),
             ),
+            const SizedBox(height: AppGap.x4),
+            TextField(
+              controller: _msgCtrl,
+              maxLines: 3,
+              minLines: 2,
+              decoration: InputDecoration(
+                hintText: '验证消息（可不填）',
+                hintStyle: const TextStyle(color: AppColors.textSecondary),
+                filled: true,
+                fillColor: AppColors.searchBg,
+                border: OutlineInputBorder(
+                  borderRadius: BorderRadius.circular(8),
+                  borderSide: BorderSide.none,
+                ),
+              ),
+            ),
             const SizedBox(height: AppGap.x6),
             SizedBox(
               height: 48,