feat: 添加 /health 健康检查端点

- 新增 GET /health 端点，公开无需认证
- 检查 PostgreSQL 数据库连接状态
- 健康时返回: {"status": "healthy", "database": "connected"}
- 不健康时返回 HTTP 503 + {"status": "unhealthy", "database": "disconnected", "error": "..."}
- 失败时记录错误到 JSON 日志
- 用于负载均衡器、Kubernetes、1Panel 健康探针
- 更新 IMPROVEMENTS.md 标记 6.3 完成

src/main.rs

@@ -680,6 +680,26 @@ async fn save_user_profile(
     }
 }
 
+// 健康检查端点
+#[get("/health")]
+async fn health_check(pool: web::Data<PgPool>) -> impl Responder {
+    // 检查数据库连接
+    match sqlx::query("SELECT 1").fetch_one(pool.get_ref()).await {
+        Ok(_) => HttpResponse::Ok().json(serde_json::json!({
+            "status": "healthy",
+            "database": "connected"
+        })),
+        Err(e) => {
+            tracing::error!("健康检查失败: {}", e);
+            HttpResponse::ServiceUnavailable().json(serde_json::json!({
+                "status": "unhealthy",
+                "database": "disconnected",
+                "error": e.to_string()
+            }))
+        }
+    }
+}
+
 fn create_server_config(
     pool: PgPool,
     http_client: Client,
@@ -698,6 +718,7 @@ fn create_server_config(
         .app_data(web::Data::new(http_client))
         .app_data(web::Data::new(app_state))
         .service(web::resource("/static/{tail:.*}").route(web::get().to(serve_static_files)))
+        .service(health_check)
         .service(login)
         .service(get_weather_details)
         .service(