feat(ai+db): 趋势分析 prompt 升级为结构化统计摘要

- 新增迁移 000093：更新 health_trend_analysis prompt，使用统计字段
  替代原始数据点遍历，引导 AI 专注 slope/R²/异常点分析
- erp-ai handler: stream_trends 改用 get_trend_analysis_data()
  替代 get_vital_signs()，传递预计算趋势特征
- sanitizer: 新增 sanitize_trend_analysis() 方法

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

@@ -104,11 +104,11 @@ where
         end: chrono::Utc::now(),
     };
 
-    let vital_dtos = state
+    let trend_data = state
         .health_provider
-        .get_vital_signs(ctx.tenant_id, patient_id, &metrics, &range)
+        .get_trend_analysis_data(ctx.tenant_id, patient_id, &metrics, &range)
         .await?;
-    let sanitized_data = state.analysis.sanitizer.sanitize_vital_signs(&vital_dtos)?;
+    let sanitized_data = state.analysis.sanitizer.sanitize_trend_analysis(&trend_data)?;
 
     let prompt = state
         .prompt