refactor(privacy-phone): 将隐私手机配置从数据库迁移至环境变量

修改 PrivacyPhoneServices 从读取数据库配置改为读取 .env 环境变量，提升配置灵活性与安全性。
更新 SQL 迁移文件，移除向系统配置表插入配置的语句，并添加配置方式说明。

app/services/other/PrivacyPhoneServices.php

@@ -34,7 +34,7 @@ class PrivacyPhoneServices extends BaseServices
      */
     public function getAppKey(): string
     {
-        return sys_config('privacy_phone_appkey', '');
+        return env('PRIVACY_PHONE.APPKEY', '');
     }
 
     /**
@@ -43,7 +43,7 @@ class PrivacyPhoneServices extends BaseServices
      */
     public function getAppSecret(): string
     {
-        return sys_config('privacy_phone_appsecret', '');
+        return env('PRIVACY_PHONE.APPSECRET', '');
     }
 
     /**
@@ -52,7 +52,7 @@ class PrivacyPhoneServices extends BaseServices
      */
     public function isEnabled(): bool
     {
-        return (bool)sys_config('privacy_phone_status', 0);
+        return (bool)env('PRIVACY_PHONE.ENABLE', false);
     }
 
     /**