refactor(common-mail): 使用 MailBuilder 替代 MailUtils

- 新增链式 MailBuilder，统一邮件发送入口
  - 删除 MailUtils，业务代码全部切换为 builder 调用
  - 默认邮件账户改为发送时获取，避免类加载阶段依赖 Bean
  - 自定义发件账号时复制默认配置，避免污染全局 MailAccount
  - 增加收件人、标题和正文参数校验
  - 调整内联图片流关闭时机，发送结束后统一关闭
  - 将 MailAccount 构建逻辑下沉到 MailProperties

ruoyi-modules/ruoyi-demo/src/main/java/org/dromara/demo/controller/MailSendController.java

@@ -2,7 +2,7 @@ package org.dromara.demo.controller;
 
 import lombok.RequiredArgsConstructor;
 import org.dromara.common.core.domain.R;
-import org.dromara.common.mail.utils.MailUtils;
+import org.dromara.common.mail.core.MailBuilder;
 import org.springframework.validation.annotation.Validated;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -32,7 +32,7 @@ public class MailSendController {
      */
     @GetMapping("/sendSimpleMessage")
     public R<Void> sendSimpleMessage(String to, String subject, String text) {
-        MailUtils.sendText(to, subject, text);
+        MailBuilder.of().to(to).subject(subject).text(text).send();
         return R.ok();
     }
 
@@ -46,7 +46,7 @@ public class MailSendController {
     @GetMapping("/sendMessageWithAttachment")
     public R<Void> sendMessageWithAttachment(String to, String subject, String text) {
         // 附件路径 禁止前端传递 有任意读取系统文件风险
-        MailUtils.sendText(to, subject, text, new File("/xxx/xxx"));
+        MailBuilder.of().to(to).subject(subject).text(text).files(new File("/xxx/xxx")).send();
         return R.ok();
     }
 
@@ -62,7 +62,7 @@ public class MailSendController {
         // 附件路径 禁止前端传递 有任意读取系统文件风险
         String[] paths = new String[]{"/xxx/xxx", "/xxx/xxx"};
         File[] array = Arrays.stream(paths).map(File::new).toArray(File[]::new);
-        MailUtils.sendText(to, subject, text, array);
+        MailBuilder.of().to(to).subject(subject).text(text).files(array).send();
         return R.ok();
     }
 

ruoyi-modules/ruoyi-workflow/src/main/java/org/dromara/workflow/service/impl/FlwCommonServiceImpl.java

@@ -11,7 +11,7 @@ import org.dromara.common.core.exception.ServiceException;
 import org.dromara.common.core.utils.SpringUtils;
 import org.dromara.common.core.utils.StreamUtils;
 import org.dromara.common.core.utils.StringUtils;
-import org.dromara.common.mail.utils.MailUtils;
+import org.dromara.common.mail.core.MailBuilder;
 import org.dromara.system.api.MessageService;
 import org.dromara.system.api.domain.PushPayloadDTO;
 import org.dromara.system.api.domain.UserDTO;
@@ -122,7 +122,7 @@ public class FlwCommonServiceImpl implements IFlwCommonService {
                             message, null, path
                         ));
                     }
-                    case EMAIL_MESSAGE -> MailUtils.sendText(emails, subject, message);
+                    case EMAIL_MESSAGE -> MailBuilder.of().to(emails).subject(subject).text(message).send();
                     case SMS_MESSAGE -> {
 //                        LinkedHashMap<String, String> map = new LinkedHashMap<>(1);
 //                        // 根据具体短信服务商参数用法传参