fix: properly remove student section without breaking tag balance

- Remove handleApplyStudent function and studentApplying state
- Remove student card section (学员身份申请提示 and 申请学员身份按钮)
- Ensure all div/Card tags remain properly balanced

web/src/components/settings/PersonalSetting.jsx

@@ -1,4 +1,4 @@
-/*
+/*
 Copyright (C) 2025 QuantumNous
 
 This program is free software: you can redistribute it and/or modify
@@ -553,17 +553,13 @@ const PersonalSetting = () => {
     }
   };
 
+
   return (
     <div className='mt-[60px]'>
       <div className='flex justify-center'>
         <div className='w-full max-w-7xl mx-auto px-2'>
           {/* 顶部用户信息区域 */}
           <UserInfoHeader t={t} userState={userState} />
-          <div className='mt-4 md:mt-6'>
-            <Card>
-              <div className='flex flex-col md:flex-row md:items-center md:justify-between gap-3'>
-                <div>
-          </div>
 
           {/* 签到日历 - 仅在启用时显示 */}
           {status?.checkin_enabled && (