feat(ai): Day 5 — ChatResponse display_hints + Web RichMessage 渲染

- ChatResponse 增加 display_hints 字段，Orchestrator 收集 Tool 产生的 DisplayHint
- DisplayHint 实现 utoipa::ToSchema
- Web ChatResponse 类型同步，DisplayHint 8 种联合类型
- RichMessage 组件：InsightCard/RiskAlert/LabReportCard/TrendChart/PatientProfile/VitalCard
- AiSidebar 消息中渲染 display_hints 富消息
- 小程序 AiChatResponse 类型同步

crates/erp-ai/src/handler/chat_handler.rs

@@ -40,6 +40,8 @@ pub struct ChatResponse {
     pub reply: String,
     pub message_id: String,
     pub iterations: usize,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub display_hints: Option<Vec<crate::agent::tool::DisplayHint>>,
 }
 
 #[utoipa::path(
@@ -252,5 +254,10 @@ where
         reply: result.reply,
         message_id,
         iterations: result.iterations,
+        display_hints: if result.display_hints.is_empty() {
+            None
+        } else {
+            Some(result.display_hints)
+        },
     })))
 }