Login Form used to display the message “未登录或登录已过期，请重新登录” twice
because the `useEffect` that inspects the `expired` query parameter was
re-executed on every re-render (e.g. language change or React StrictMode’s
double-mount in development).
### What's changed
• **LoginForm.js** – `useEffect` that shows the toast now has an empty
dependency array so it runs only once on initial mount.
• Reviewed **PasswordResetConfirm.js**, **PasswordResetForm.js** and
**RegisterForm.js** and confirmed they do not contain the same issue;
no changes were required.
### Impact
Users now see the “session expired” notification exactly once, removing
confusion and improving the overall UX.
