feat: 网关只读资产改为数据表，只读资产只允许查询类调用

- 新增 tb_gateway_readonly_card（卡 ICCID / 设备 IMEI）与开关 JUNHONG_GATEWAY_READONLY_ENABLED，
  替换环境变量名单 JUNHONG_GATEWAY_READONLY_ICCIDS
- 只读资产只放行查卡状态、查实名、查流量、查设备信息、查设备槽位、同步设备状态；
  停机、复机、限速、实名认证链接与设备写操作在网关出口本地拦截；查表失败按拦截；不缓存
- 测试环境部署开启只读模式；新增技术方案与清理顺序文档

Change: add-gateway-readonly-prod-import

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pkg/config/loader.go

@@ -130,7 +130,7 @@ func bindEnvVariables(v *viper.Viper) {
 		"gateway.app_id",
 		"gateway.app_secret",
 		"gateway.timeout",
-		"gateway.readonly_iccids",
+		"gateway.readonly_enabled",
 		"polling.verbose_log",
 		"polling.carrier.nsqd_address",
 		"polling.carrier.nsqlookupd_addresses",