feat: 聊天卡片升级+趋势图重写+智能体欢迎卡片

- AgentWelcomeCard：紫色渐变头部+快捷按钮网格+智能体描述
- DataConfirmCard：绿色渐变确认条+迷你趋势图+编辑/确认按钮
- MedicationConfirmCard：药丸图标+剩余药量进度条+确认/跳过
- DietAnalysisCard：大号热量+营养素圆环+食物明细+AI建议
- ReportAnalysisCard：指标表格+异常高亮+AI解读
- trend_page 重写：CustomPaint 平滑曲线+当前值卡片+统计摘要
- chat_provider 新增 agentWelcome 消息类型

health_app/lib/providers/chat_provider.dart

@@ -4,7 +4,7 @@ import 'auth_provider.dart';
 import 'data_providers.dart';
 import '../utils/sse_handler.dart';
 
-enum MessageType { text, dataConfirm, medicationConfirm, dietAnalysis, reportAnalysis, quickOptions }
+enum MessageType { text, dataConfirm, medicationConfirm, dietAnalysis, reportAnalysis, quickOptions, agentWelcome }
 
 class ChatMessage {
   final String id;
@@ -236,6 +236,7 @@ class ChatNotifier extends Notifier<ChatState> {
       case 'diet_analysis': return MessageType.dietAnalysis;
       case 'report_analysis': return MessageType.reportAnalysis;
       case 'quick_options': return MessageType.quickOptions;
+      case 'agent_welcome': return MessageType.agentWelcome;
       default: return MessageType.text;
     }
   }