refactor: 移除全局单例、修复分层违规、统一错误与响应

internal/handler/swagger_test.go

@@ -12,7 +12,8 @@ import (
 func TestHealthCheck_Degraded(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	router := gin.New()
-	router.GET("/health", HealthCheck)
+	// 传入 nil 依赖，模拟服务不可用场景
+	router.GET("/health", NewHealthCheck(nil, nil))
 
 	req := httptest.NewRequest(http.MethodGet, "/health", nil)
 	w := httptest.NewRecorder()
@@ -22,6 +23,3 @@ func TestHealthCheck_Degraded(t *testing.T) {
 		t.Fatalf("expected 503 when dependencies missing, got %d", w.Code)
 	}
 }
-
-
-