fix: 7处修复 - 溢出/黑屏/趋势图/欢迎卡片/抽屉

health_app/lib/providers/chat_provider.dart

@@ -145,6 +145,17 @@ class ChatNotifier extends Notifier<ChatState> {
     state = state.activeAgent == a ? const ChatState() : ChatState(activeAgent: a);
   }
 
+  void insertAgentWelcome(ActiveAgent agent) {
+    state = state.copyWith(messages: [...state.messages, ChatMessage(
+      id: 'welcome_${agent.name}_${DateTime.now().millisecondsSinceEpoch}',
+      role: 'assistant',
+      content: '',
+      createdAt: DateTime.now(),
+      type: MessageType.agentWelcome,
+      metadata: {'agent': agent.name},
+    )]);
+  }
+
   Future<void> sendMessage(String text) async {
     if (text.trim().isEmpty || state.isStreaming) return;