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/chat_screen.dart

@@ -12,6 +12,7 @@ import 'package:path_provider/path_provider.dart';
 
 import '../services/call_service.dart';
 import '../services/im_service.dart';
+import '../services/message_send_service.dart';
 import '../theme.dart';
 import '../utils/format.dart';
 import '../widgets/chat_input_bar.dart';
@@ -135,6 +136,8 @@ class _ChatScreenState extends State<ChatScreen> {
 
   // ---------------- 发送 ----------------
 
+  /// 统一发送入口：文字/表情/语音/图片/文件都经过这里。
+  /// 失败时用 [MessageSendService] 的中文提示，不再只标红感叹号。
   Future<void> _sendMessage(Message message) async {
     setState(() {
       message.status = MessageStatus.sending;
@@ -142,17 +145,17 @@ class _ChatScreenState extends State<ChatScreen> {
     });
     if (_scroll.hasClients) _scroll.jumpTo(0);
     try {
-      final sent = await OpenIM.iMManager.messageManager.sendMessage(
+      final sent = await MessageSendService.instance.send(
         message: message,
         userID: _isGroup ? null : _peerID,
         groupID: _isGroup ? _groupID : null,
-        offlinePushInfo: OfflinePushInfo(),
       );
       if (!mounted) return;
       setState(() => message.status = sent.status ?? MessageStatus.succeeded);
-    } catch (_) {
+    } catch (e) {
       if (!mounted) return;
       setState(() => message.status = MessageStatus.failed);
+      _toast(e is Exception ? e.toString() : '消息没发出去，请重试');
     }
   }
 
@@ -160,17 +163,17 @@ class _ChatScreenState extends State<ChatScreen> {
   Future<void> _resend(Message message) async {
     setState(() => message.status = MessageStatus.sending);
     try {
-      final sent = await OpenIM.iMManager.messageManager.sendMessage(
+      final sent = await MessageSendService.instance.send(
         message: message,
         userID: _isGroup ? null : _peerID,
         groupID: _isGroup ? _groupID : null,
-        offlinePushInfo: OfflinePushInfo(),
       );
       if (!mounted) return;
       setState(() => message.status = sent.status ?? MessageStatus.succeeded);
-    } catch (_) {
+    } catch (e) {
       if (!mounted) return;
       setState(() => message.status = MessageStatus.failed);
+      _toast(e is Exception ? e.toString() : '消息没发出去，请重试');
     }
   }