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/home/ui/screens/home_screen.dart

@@ -16,8 +16,6 @@ const _defaultPadding = 20.0;
 const _itemSpacing = 16.0;
 const _inputPadding = 16.0;
 const _iconSize = 24.0;
-const _avatarSize = 32.0;
-const _botIconSize = 18.0;
 const _messagePaddingH = 13.0;
 const _messagePaddingV = 9.0;
 const _cornerRadius = 12.0;
@@ -39,6 +37,7 @@ class HomeScreen extends StatefulWidget {
 class _HomeScreenState extends State<HomeScreen> {
   final TextEditingController _messageController = TextEditingController();
   final ScrollController _scrollController = ScrollController();
+  late final ChatBloc _chatBloc;
 
   bool get _hasMessage => _messageController.text.trim().isNotEmpty;
 
@@ -46,6 +45,8 @@ class _HomeScreenState extends State<HomeScreen> {
   void initState() {
     super.initState();
     _messageController.addListener(_onMessageChanged);
+    _chatBloc = ChatBloc();
+    _chatBloc.loadHistory();
   }
 
   @override
@@ -53,6 +54,7 @@ class _HomeScreenState extends State<HomeScreen> {
     _messageController.removeListener(_onMessageChanged);
     _messageController.dispose();
     _scrollController.dispose();
+    _chatBloc.close();
     super.dispose();
   }
 
@@ -62,8 +64,8 @@ class _HomeScreenState extends State<HomeScreen> {
 
   @override
   Widget build(BuildContext context) {
-    return BlocProvider(
-      create: (context) => ChatBloc(),
+    return BlocProvider.value(
+      value: _chatBloc,
       child: BlocConsumer<ChatBloc, ChatState>(
         listener: (context, state) {
           if (state.error != null) {
@@ -132,6 +134,10 @@ class _HomeScreenState extends State<HomeScreen> {
   }
 
   Widget _buildChatArea(BuildContext context, ChatState state) {
+    if (state.isLoading && state.items.isEmpty) {
+      return const Center(child: CircularProgressIndicator());
+    }
+
     if (state.items.isEmpty) {
       return const Center(
         child: Text(
@@ -141,30 +147,96 @@ class _HomeScreenState extends State<HomeScreen> {
       );
     }
 
-    WidgetsBinding.instance.addPostFrameCallback((_) {
-      if (_scrollController.hasClients) {
-        _scrollController.animateTo(
-          _scrollController.position.maxScrollExtent,
-          duration: const Duration(milliseconds: _scrollDurationMs),
-          curve: Curves.easeOut,
-        );
-      }
-    });
+    return RefreshIndicator(
+      onRefresh: () => _onRefresh(context),
+      child: ListView.builder(
+        controller: _scrollController,
+        physics: const AlwaysScrollableScrollPhysics(),
+        padding: const EdgeInsets.all(_defaultPadding),
+        itemCount: state.items.length + (state.hasEarlierHistory ? 1 : 0),
+        itemBuilder: (context, index) {
+          if (index == 0 && state.hasEarlierHistory) {
+            return _buildLoadMoreButton(context, state.isLoading);
+          }
 
-    return ListView.builder(
-      controller: _scrollController,
-      padding: const EdgeInsets.all(_defaultPadding),
-      itemCount: state.items.length,
-      itemBuilder: (context, index) {
-        final item = state.items[index];
-        return Padding(
-          padding: const EdgeInsets.only(bottom: _itemSpacing),
-          child: _buildChatItem(item),
-        );
-      },
+          final itemIndex = state.hasEarlierHistory ? index - 1 : index;
+          final item = state.items[itemIndex];
+
+          final showDateDivider =
+              itemIndex == 0 ||
+              !_isSameDay(state.items[itemIndex - 1].timestamp, item.timestamp);
+
+          return Column(
+            crossAxisAlignment: CrossAxisAlignment.stretch,
+            children: [
+              if (showDateDivider) _buildDateDivider(item.timestamp),
+              Padding(
+                padding: const EdgeInsets.only(bottom: _itemSpacing),
+                child: _buildChatItem(item),
+              ),
+            ],
+          );
+        },
+      ),
     );
   }
 
+  bool _isSameDay(DateTime a, DateTime b) {
+    return a.year == b.year && a.month == b.month && a.day == b.day;
+  }
+
+  Widget _buildDateDivider(DateTime date) {
+    final now = DateTime.now();
+    final weekdays = ['周一', '周二', '周三', '周四', '周五', '周六', '周日'];
+    final weekday = weekdays[date.weekday - 1];
+
+    // For all dates (today/yesterday/this year), use the same format
+    // Only add year prefix for dates from previous years
+    final label = date.year == now.year
+        ? '${date.month}月${date.day}日 $weekday'
+        : '${date.year}年${date.month}月${date.day}日 $weekday';
+
+    return Container(
+      padding: const EdgeInsets.symmetric(vertical: 12),
+      alignment: Alignment.center,
+      child: Text(
+        label,
+        style: const TextStyle(fontSize: 12, color: AppColors.slate400),
+      ),
+    );
+  }
+
+  Widget _buildLoadMoreButton(BuildContext context, bool isLoading) {
+    return GestureDetector(
+      onTap: isLoading ? null : () => _onLoadMore(context),
+      child: Container(
+        padding: const EdgeInsets.symmetric(vertical: 8),
+        alignment: Alignment.center,
+        child: isLoading
+            ? const SizedBox(
+                width: 14,
+                height: 14,
+                child: CircularProgressIndicator(
+                  strokeWidth: 1.5,
+                  color: AppColors.slate400,
+                ),
+              )
+            : const Text(
+                '查看历史',
+                style: TextStyle(fontSize: 12, color: AppColors.slate400),
+              ),
+      ),
+    );
+  }
+
+  Future<void> _onRefresh(BuildContext context) async {
+    await context.read<ChatBloc>().loadMoreHistory();
+  }
+
+  void _onLoadMore(BuildContext context) {
+    context.read<ChatBloc>().loadMoreHistory();
+  }
+
   Widget _buildChatItem(ChatListItem item) {
     switch (item.type) {
       case ChatItemType.message:
@@ -182,24 +254,8 @@ class _HomeScreenState extends State<HomeScreen> {
       mainAxisAlignment: isUser
           ? MainAxisAlignment.end
           : MainAxisAlignment.start,
-      crossAxisAlignment: CrossAxisAlignment.center,
+      crossAxisAlignment: CrossAxisAlignment.start,
       children: [
-        if (!isUser) ...[
-          Container(
-            width: _avatarSize,
-            height: _avatarSize,
-            decoration: BoxDecoration(
-              color: AppColors.blue100,
-              shape: BoxShape.circle,
-            ),
-            child: const Icon(
-              LucideIcons.bot,
-              size: _botIconSize,
-              color: AppColors.blue600,
-            ),
-          ),
-          const SizedBox(width: 8),
-        ],
         Flexible(
           child: Container(
             padding: const EdgeInsets.symmetric(
@@ -222,8 +278,6 @@ class _HomeScreenState extends State<HomeScreen> {
             ),
           ),
         ),
-        if (isUser) const SizedBox(width: 40),
-        if (!isUser) const SizedBox(width: 40),
       ],
     );
   }
@@ -365,6 +419,16 @@ class _HomeScreenState extends State<HomeScreen> {
     if (content.isEmpty) return;
     _messageController.clear();
     context.read<ChatBloc>().sendMessage(content);
+
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (_scrollController.hasClients) {
+        _scrollController.animateTo(
+          _scrollController.position.maxScrollExtent,
+          duration: const Duration(milliseconds: _scrollDurationMs),
+          curve: Curves.easeOut,
+        );
+      }
+    });
   }
 
   void _showBottomSheet(BuildContext context) {