feat: 二级页面色彩刷新 + 用药/通知/设备重构 + 后端健康档案/通知管线增强 + 大量测试

## 后端
- 健康档案: 新增手术状态字段 + EF 迁移; HealthArchiveService 新增查询方法
- 健康记录: HealthRecordService 新增批量/统计方法; 契约扩展
- 用药: 新增 MedicationScheduleStatus 枚举; MedicationService 排班逻辑调整
- 通知: EfUserNotificationPipeline 重构; 新增 EfReminderCatchUpService; 通知管线支持更多场景
- 用户: UserService 账号删除逻辑; 新增 local_account_file_cleanup; EfUserRepository 扩展
- AI: medication_agent_handler 微调; prompt_manager 优化; AiConversationService 上下文处理
- Endpoint: doctor/medication/exercise/health/notification/user 等多接口调整
- BackgroundService: health_record_reminder_service 重构, 提醒补漏逻辑
- 测试: 新增 account_deletion/doctor_endpoint/medication_schedule/medication_update/prompt_manager 测试

## 前端
- UI 系统: app_theme 大幅重构; app_colors/app_design_tokens/app_module_visuals 调整; 二级页面色彩刷新
- 主页: home_page 背景渐变 + 消息列表提取 _HomeMessages + 通知检查逻辑; chat_messages_view 全面重构
- 用药: medication_list/edit/checkin 三页重构, 新增 medication_ui_logic 抽取
- 通知: notification_prefs_page 重构, 新增 notification_prefs_logic; notification_center 优化
- 设备: device_management 重构, 新增 device_sync_ui_logic; device_scan 优化
- 趋势图: trend_page 大幅重构
- 登录: login_page 重构
- 个人资料: 新增 profile_edit_page; profile_page 优化
- 运动: 新增 exercise/ 目录 + care_plan_ui_logic
- 其他: remaining_pages/report_pages/health_drawer/admin/doctor 等多页面调整
- 组件: common_widgets/app_empty_state/app_error_state/app_future_view/app_toast/ai_content 优化
- Provider: chat_provider/consultation_provider/data_providers/auth_provider 调整
- AndroidManifest: 移除多余权限
- 测试: 新增 ai_content/care_plan/home_message/login_flow/medication_checkin/medication_ui/notification_prefs/profile_device/secondary_page/swipe_delete 等大量测试

## 文档
- 新增 ui-design-system.md 设计系统文档
- 新增 secondary-page-color-refresh 计划 + specs 目录

health_app/lib/providers/chat_provider.dart

@@ -40,31 +40,39 @@ enum ActiveAgent {
   exercise,
 }
 
+const _keepConversationId = Object();
+
 class ChatState {
   final ActiveAgent activeAgent;
   final List<ChatMessage> messages;
   final String? conversationId;
   final bool isStreaming;
   final String? thinkingText;
+  final bool isViewingHistory;
   const ChatState({
     this.activeAgent = ActiveAgent.default_,
     this.messages = const [],
     this.conversationId,
     this.isStreaming = false,
     this.thinkingText,
+    this.isViewingHistory = false,
   });
   ChatState copyWith({
     ActiveAgent? activeAgent,
     List<ChatMessage>? messages,
-    String? conversationId,
+    Object? conversationId = _keepConversationId,
     bool? isStreaming,
     String? thinkingText,
+    bool? isViewingHistory,
   }) => ChatState(
     activeAgent: activeAgent ?? this.activeAgent,
     messages: messages ?? this.messages,
-    conversationId: conversationId ?? this.conversationId,
+    conversationId: identical(conversationId, _keepConversationId)
+        ? this.conversationId
+        : conversationId as String?,
     isStreaming: isStreaming ?? this.isStreaming,
     thinkingText: thinkingText ?? this.thinkingText,
+    isViewingHistory: isViewingHistory ?? this.isViewingHistory,
   );
 }
 
@@ -77,6 +85,7 @@ class ChatNotifier extends Notifier<ChatState> {
   Completer<void>? _streamDone;
   ActiveAgent? _lastTriggeredAgent;
   Timer? _agentTapLockTimer;
+  bool _loadingConversation = false;
 
   /// 重置整个会话：取消正在进行的 SSE，清空消息和会话 ID。
   /// 历史记录页一键清空 / 删除当前会话时调用。
@@ -162,42 +171,17 @@ class ChatNotifier extends Notifier<ChatState> {
     );
   }
 
-  /// 根据 AI 调用的工具自动切换智能体胶囊
-  void _switchAgentByTool(String tool) {
-    ActiveAgent? agent;
-    switch (tool) {
-      case 'record_health_data':
-      case 'query_health_records':
-        agent = ActiveAgent.health;
-        break;
-      case 'estimate_food_text':
-        agent = ActiveAgent.diet;
-        break;
-      case 'manage_medication':
-        agent = ActiveAgent.medication;
-        break;
-      case 'manage_exercise':
-        agent = ActiveAgent.exercise;
-        break;
-      case 'request_doctor':
-        agent = ActiveAgent.consultation;
-        break;
-      case 'analyze_report':
-        agent = ActiveAgent.report;
-        break;
-    }
-    if (agent != null) {
-      state = state.copyWith(activeAgent: agent);
-    }
-  }
-
   Future<String?> loadConversation(String convId) async {
+    if (state.isStreaming) return '小脉正在回复，请稍后再切换对话';
+    if (_loadingConversation) return '正在加载其他对话，请稍候';
+    _loadingConversation = true;
     await _cancelActiveStream();
     _cancelPendingAgentWelcome();
     try {
       final api = ref.read(apiClientProvider);
       final res = await api.get('/api/ai/conversations/$convId');
       final rawMessages = (res.data['data'] as List?) ?? [];
+      if (rawMessages.isEmpty) return '该对话已不存在，请刷新记录';
       final messages = rawMessages.map((m) {
         final map = m as Map<String, dynamic>;
         final role = map['role']?.toString().toLowerCase() == 'user'
@@ -218,14 +202,18 @@ class ChatNotifier extends Notifier<ChatState> {
         );
       }).toList();
 
-      state = state.copyWith(
+      state = ChatState(
         messages: messages,
         conversationId: convId,
         activeAgent: ActiveAgent.default_,
+        isViewingHistory: true,
       );
+      _lastTriggeredAgent = null;
       return null;
     } catch (_) {
       return '会话加载失败，请稍后重试';
+    } finally {
+      _loadingConversation = false;
     }
   }
 
@@ -234,6 +222,7 @@ class ChatNotifier extends Notifier<ChatState> {
   /// 重复点击同一胶囊不重复弹卡片
   void triggerAgent(ActiveAgent agent, String label) {
     if (_agentTapLockTimer != null || _lastTriggeredAgent == agent) return;
+    _resumeConversationFromHistory();
     _lastTriggeredAgent = agent;
 
     final now = DateTime.now();
@@ -272,6 +261,7 @@ class ChatNotifier extends Notifier<ChatState> {
     if (!await file.exists()) return;
     _lastTriggeredAgent = null;
     _cancelPendingAgentWelcome();
+    _resumeConversationFromHistory();
 
     // 先显示用户消息（本地显示图片路径）
     final userMsg = ChatMessage(
@@ -338,6 +328,7 @@ class ChatNotifier extends Notifier<ChatState> {
     if (!await file.exists()) return;
     _lastTriggeredAgent = null;
     _cancelPendingAgentWelcome();
+    _resumeConversationFromHistory();
 
     final userMsg = ChatMessage(
       id: '${DateTime.now().millisecondsSinceEpoch}',
@@ -392,6 +383,7 @@ class ChatNotifier extends Notifier<ChatState> {
     if (text.trim().isEmpty || state.isStreaming) return;
     _lastTriggeredAgent = null;
     _cancelPendingAgentWelcome();
+    _resumeConversationFromHistory();
 
     final userMsg = ChatMessage(
       id: '${DateTime.now().millisecondsSinceEpoch}',
@@ -470,6 +462,11 @@ class ChatNotifier extends Notifier<ChatState> {
     }
   }
 
+  void _resumeConversationFromHistory() {
+    if (!state.isViewingHistory) return;
+    state = state.copyWith(isViewingHistory: false);
+  }
+
   Future<void> _cancelActiveStream() async {
     await _subscription?.cancel();
     _subscription = null;
@@ -496,7 +493,10 @@ class ChatNotifier extends Notifier<ChatState> {
     final a = j['action'] as String?;
     switch (a) {
       case 'conversation_id':
-        state = state.copyWith(conversationId: j['data']?.toString());
+        state = state.copyWith(
+          conversationId: j['data']?.toString(),
+          isViewingHistory: false,
+        );
       case 'answer':
         final messageType = j['type'] as String? ?? 'text';
         aiMsg.type = _parseMessageType(messageType);
@@ -510,8 +510,6 @@ class ChatNotifier extends Notifier<ChatState> {
         state = state.copyWith(thinkingText: j['message'] as String?);
       case 'tool_result':
         final tool = j['tool'] as String? ?? '';
-        // 根据 AI 调用的工具自动切换智能体胶囊
-        _switchAgentByTool(tool);
         if (tool == 'record_health_data') {
           ref.invalidate(latestHealthProvider);
         }