fix(mail2925): 修复验证码轮询与登录态复用逻辑并清理中文文案，重构 sidepanel：统一 Hotmail 和 2925 号池表单交互

- 抽出共享 account-pool-ui helper
- 统一添加账号、取消添加、批量导入交互
- 调整号池列表收起高度与按钮布局
- 补充测试并同步更新项目文档

tests/background-mail2925-relogin-wait.test.js

@@ -78,5 +78,5 @@ test('ensureMail2925MailboxSession waits 3 seconds before and after opening logi
 
   assert.deepStrictEqual(events.openedUrls, ['https://2925.com/login/']);
   assert.deepStrictEqual(events.sleeps, [3000, 3000]);
-  assert.equal(events.readyCalls, 1);
+  assert.equal(events.readyCalls, 2);
 });