💄refactor: enhance EditUser and AddUser form validation & UX

Changes in `web/src/pages/User/EditUser.js`:
• Added `rules` to
  – `Form.Select group`: now required with error “Please select group”.
  – `Form.InputNumber quota`: now required with error “Please enter quota”.
• Added `step={500000}` to quota `InputNumber` for quicker numeric input.
• Replaced invalid `readonly` with React-correct `readOnly`, and added descriptive placeholders for all binding-info fields (GitHub/OIDC/WeChat/Email/Telegram).
• Removed unused `downloadTextAsFile` import.

These updates tighten form validation, improve data entry ergonomics, and restore clear read-only indicators for third-party bindings.

web/src/pages/TopUp/index.js

@@ -931,7 +931,7 @@ const TopUp = () => {
                 <Title heading={6}>{t('邀请链接')}</Title>
                 <Input
                   value={affLink}
-                  readOnly
+                  readonly
                   size='large'
                   suffix={
                     <Button