feat(ai+health): 闭环核心 — 随访完成→再分析触发 + 前后对比报告

- follow_up.completed 消费者：通过 action_result 反查 AI 建议，触发再分析
- ai.reanalysis.requested 消费者：加载原始建议 baseline
- comparison.rs：对比报告生成引擎（指标变化百分比+趋势判断）
- GET /ai/suggestions/{id}/comparison：前后对比报告 API
- find_by_followup_task：通过随访任务反查关联建议ID

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

@@ -87,3 +87,43 @@ where
         "status": new_status.as_str(),
     }))))
 }
+
+/// 获取 AI 建议的前后对比报告。
+pub async fn get_comparison<S>(
+    State(state): State<AiState>,
+    Extension(ctx): Extension<TenantContext>,
+    Path(id): Path<uuid::Uuid>,
+) -> Result<Json<ApiResponse<serde_json::Value>>, erp_core::error::AppError>
+where
+    AiState: FromRef<S>,
+    S: Clone + Send + Sync + 'static,
+{
+    require_permission(&ctx, "ai.suggestion.list")?;
+
+    use crate::entity::ai_suggestion;
+    use sea_orm::{ColumnTrait, EntityTrait, QueryFilter};
+
+    let suggestion = ai_suggestion::Entity::find_by_id(id)
+        .one(&state.db)
+        .await
+        .map_err(|e| erp_core::error::AppError::Internal(e.to_string()))?
+        .filter(|s| s.tenant_id == ctx.tenant_id && s.deleted_at.is_none())
+        .ok_or_else(|| erp_core::error::AppError::NotFound("建议不存在".into()))?;
+
+    match &suggestion.baseline_snapshot {
+        Some(bs) if !bs.is_null() => {
+            let action_result = suggestion.action_result.as_ref().unwrap_or(&serde_json::Value::Null);
+            Ok(Json(ApiResponse::ok(serde_json::json!({
+                "suggestion_id": id,
+                "baseline": bs,
+                "current": action_result,
+                "comparison_available": !action_result.is_null(),
+            }))))
+        }
+        _ => Ok(Json(ApiResponse::ok(serde_json::json!({
+            "suggestion_id": id,
+            "comparison_available": false,
+            "message": "该建议暂无 baseline 快照，无法生成对比报告",
+        })))),
+    }
+}