💄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/Home/index.js

@@ -130,7 +130,7 @@ const Home = () => {
                   {/* BASE URL 与端点选择 */}
                   <div className="flex flex-col md:flex-row items-center justify-center gap-4 w-full mt-4 md:mt-6 max-w-md">
                     <Input
-                      readOnly
+                      readonly
                       value={serverAddress}
                       className="flex-1 !rounded-full"
                       size={isMobile() ? 'default' : 'large'}