fix: 收敛 2925 邮箱修复范围

- 回退非必要的 2925 行为改动，仅保留已验证有效的修复
- 保留 bounce 转发地址解析、中文日期解析与邮箱页复用时的 ready 恢复
- 同步最小化测试断言，保持当前代码与测试一致

background/steps/fetch-signup-code.js

@@ -26,10 +26,6 @@
     } = deps;
 
     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 : [];