feat(attendance): enforce captcha validation before check-in

- require a successful captcha challenge before recording the day’s attendance
- preserve the original attendance summary layout after a successful check-in

Signed-off-by: Qi HU <github@spcsky.com>

lang/cht/lang_attendance.php

@@ -13,4 +13,5 @@ $lang_attendance = array
     'retroactive_event_text' => '補',
     'retroactive_confirm_tip' => '確定要補簽: ',
     'retroactive_description' => '點擊白色背景的圓點進行補簽。你目前擁有補簽卡 <b>%d</b> 張。',
+    'attend_button' => '立即簽到',
 );