fix(v0.11): 第二轮走查 P1/P2（按模块优先级）

- davinci：DavinciResult.fail/success；FileManager Feign Fallback 结构化降级；FileStorageManagerImpl 对空 Result/Response 防御
- cwos-resource：RestPortalUserServiceImpl 消除静默 null，统一 CloudwalkResult.fail 与 getDefaultPwd 空串语义
- device-manager：DeviceConstant 改为 final 工具类
- aks：AksRespCodeConstant final + 私有构造
- ninca-crk：启动入口 SLF4J、显式 Feign 扫描包、SpringApplication 写法
- ninca-qk-alarm：main 简化、收窄 @EnableFeignClients（保持 netflix 注解以兼容当前 BOM）

Made-with: Cursor

maven-cloudwalk-intelligent-davinci-manager/davinci-manager-common/src/main/java/cn/cloudwalk/intelligent/davinci/common/result/DavinciResult.java

@@ -42,4 +42,22 @@ public class DavinciResult<T> implements Serializable {
     public void setData(T data) {
         this.data = data;
     }
+
+    /** Feign 降级或本地失败路径使用的结构化失败体（不走异常控制流）。 */
+    public static <T> DavinciResult<T> fail(String code, String message) {
+        DavinciResult<T> r = new DavinciResult<>();
+        r.setSuccess(false);
+        r.setCode(code);
+        r.setMessage(message);
+        return r;
+    }
+
+    public static <T> DavinciResult<T> success(T data) {
+        DavinciResult<T> r = new DavinciResult<>();
+        r.setSuccess(true);
+        r.setCode("0");
+        r.setMessage("ok");
+        r.setData(data);
+        return r;
+    }
 }