fix: 修复 2925 收件模式轮询与重复注入

- receive 模式下跳过 2925 邮箱页顶部账号校验
- 解析 bounce 转发地址与中文日期，避免误过滤验证码邮件
- 为内容脚本增加重复注入保护，避免重复声明导致轮询失效

background/steps/fetch-login-code.js

@@ -69,6 +69,10 @@
     }
 
     function getExpectedMail2925MailboxEmail(state = {}) {
+      if (String(state?.mail2925Mode || '').trim().toLowerCase() === 'receive') {
+        return '';
+      }
+
       if (Boolean(state?.mail2925UseAccountPool)) {
         const currentAccountId = String(state?.currentMail2925AccountId || '').trim();
         const accounts = Array.isArray(state?.mail2925Accounts) ? state.mail2925Accounts : [];