feat(chat): 正在输入指示器 — 点对点复刻 iOS + 性能改进

## 新增
- TypingIndicatorManager: 内存态管理器，精准Timer替代iOS 1s轮询
- TypingInputSender: per-chatId 节流(3s)/防抖(2s)，修复iOS跨chat竞态
- WS chat_input/chat_typing 帧处理（mode2 + ctl 双路径）

## UI
- ChatDetailPage AppBar 绿色副标题显示"正在输入…"
- ChatPage 列表 snippet 绿色输入状态优先于 lastMsg
- 群聊不发送 typing 事件（对齐 iOS gate）

## 改进 (vs iOS)
- Timer 仅在有 entry 时启动，空时 null（零空转）
- per-chatId 隔离节流/防抖（iOS 全局共享有竞态 bug）
- msgIdx 守卫防止乱序帧覆盖 lastMsg

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/im_app/lib/features/chat/view/chat_page.dart

@@ -1,8 +1,10 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import 'package:im_app/app/di/app_providers.dart';
 import 'package:im_app/domain/entities/chat.dart';
 import 'package:im_app/features/chat/di/chat_provider.dart';
+import 'package:im_app/features/chat/di/chat_service_providers.dart';
 import 'package:im_app/features/chat/presentation/chat_list_view_model.dart';
 
 /// 聊天列表页
@@ -16,6 +18,8 @@ class ChatPage extends ConsumerWidget {
   Widget build(BuildContext context, WidgetRef ref) {
     final vm = ref.watch(chatListViewModelProvider.notifier);
     final chatsAsync = ref.watch(allChatsProvider);
+    // 监听输入状态变化 → 触发列表重建（对齐 iOS @Published typing 全局更新）
+    ref.watch(typingChangeProvider);
 
     return Scaffold(
       appBar: AppBar(
@@ -45,20 +49,29 @@ class ChatPage extends ConsumerWidget {
   }
 }
 
-class _ChatTile extends StatelessWidget {
+class _ChatTile extends ConsumerWidget {
   const _ChatTile({required this.chat, required this.vm});
 
   final Chat chat;
   final ChatListViewModel vm;
 
   @override
-  Widget build(BuildContext context) {
+  Widget build(BuildContext context, WidgetRef ref) {
     final name = chat.name ?? 'Chat ${chat.chatId ?? chat.id}';
     final lastMsg = chat.lastMsg ?? '';
     final unread = chat.unreadNum ?? 0;
     final sendTime = chat.lastTime;
     final timeStr = sendTime != null ? _formatTime(sendTime) : '';
 
+    // 正在输入状态（对齐 iOS ConversationCell.typingText）
+    final chatId = chat.chatId ?? chat.id;
+    final myUid = ref.watch(authNotifierProvider).currentUid ?? 0;
+    final typingMgr = ref.watch(typingIndicatorManagerProvider);
+    final isGroup = (chat.typ ?? 1) == 2;
+    final typingText = isGroup
+        ? typingMgr.groupDisplayText(chatId: chatId, myUserId: myUid)
+        : typingMgr.displayText(chatId: chatId, myUserId: myUid);
+
     return ListTile(
       leading: CircleAvatar(
         backgroundColor: Theme.of(context).colorScheme.primaryContainer,
@@ -86,14 +99,24 @@ class _ChatTile extends StatelessWidget {
       subtitle: Row(
         children: [
           Expanded(
-            child: Text(
-              lastMsg,
-              maxLines: 1,
-              overflow: TextOverflow.ellipsis,
-              style: Theme.of(context).textTheme.bodySmall?.copyWith(
-                    color: Theme.of(context).colorScheme.outline,
+            child: typingText != null
+                // 输入状态优先显示（绿色，对齐 iOS onlineGreen）
+                ? Text(
+                    typingText,
+                    maxLines: 1,
+                    overflow: TextOverflow.ellipsis,
+                    style: Theme.of(context).textTheme.bodySmall?.copyWith(
+                          color: Colors.green.shade600,
+                        ),
+                  )
+                : Text(
+                    lastMsg,
+                    maxLines: 1,
+                    overflow: TextOverflow.ellipsis,
+                    style: Theme.of(context).textTheme.bodySmall?.copyWith(
+                          color: Theme.of(context).colorScheme.outline,
+                        ),
                   ),
-            ),
           ),
           if (unread > 0)
             Container(