refactor(chat): 重构聊天模块并集成历史消息加载功能

- 删除冗余的 chat_history_repository 和 home_mock_data
- 简化 ag_ui_event fromJson 使用工厂映射表
- 提取 ChatBloc 事件处理方法，添加 loadHistory/loadMoreHistory
- HomeScreen 集成 ChatBloc 实现历史消息加载和下拉刷新
- 更新 AGENTS.md 文档约束

apps/lib/features/chat/data/services/ag_ui_service.dart

@@ -44,8 +44,6 @@ class AgUiService {
   Future<void> loadHistory({DateTime? beforeDate}) async {
     if (Env.isMockApi) {
       await _mockLoadHistory(beforeDate: beforeDate);
-    } else {
-      throw UnimplementedError('Real API not implemented');
     }
   }
 
@@ -58,8 +56,10 @@ class AgUiService {
     final runId = '$_runIdPrefix${DateTime.now().millisecondsSinceEpoch}';
 
     onEvent(RunStartedEvent(threadId: threadId, runId: runId));
+    await Future.delayed(const Duration(milliseconds: 10));
 
-    DateTime targetDate;
+    // Determine target date, end early if no earlier history
+    final DateTime targetDate;
     if (beforeDate != null) {
       final prevDate = _historyService.getPreviousDay(beforeDate);
       if (prevDate == null) {
@@ -72,9 +72,8 @@ class AgUiService {
     }
 
     final messages = _historyService.getHistoryForDay(targetDate);
-
     onEvent(MessagesSnapshotEvent(messages: messages));
-
+    await Future.delayed(const Duration(milliseconds: 10));
     onEvent(RunFinishedEvent(threadId: threadId, runId: runId));
   }