fix: resolve critical security and UI session mismatch by clearing React Query cache on login/logout and invalidating on subscription updates

frontend/src/app/auth/login/LoginForm.tsx

@@ -1,6 +1,7 @@
 'use client';
 
 import { useState, useEffect, useCallback } from 'react';
+import { useQueryClient } from '@tanstack/react-query';
 import Link from 'next/link';
 import { useRouter, useSearchParams } from 'next/navigation';
 import { Eye, EyeOff, Mail, Lock, ArrowRight, Loader2, Languages } from 'lucide-react';
@@ -31,6 +32,8 @@ export function LoginForm() {
 
   const { clientId: googleClientId, enabled: googleEnabled } = useGoogleConfig();
 
+  const queryClient = useQueryClient();
+
   useEffect(() => {
     if (loginMutation.isError && loginMutation.error) {
       notify({
@@ -39,7 +42,7 @@ export function LoginForm() {
         variant: 'destructive',
       });
     }
-  }, [loginMutation.isError, loginMutation.error, notify]);
+  }, [loginMutation.isError, loginMutation.error, notify, t]);
 
   const handleSubmit = (e: React.FormEvent) => {
     e.preventDefault();
@@ -55,6 +58,7 @@ export function LoginForm() {
         { credential: credentialResponse.credential },
       );
       const { access_token, refresh_token } = response.data;
+      queryClient.clear();
       localStorage.setItem('token', access_token);
       localStorage.setItem('refresh_token', refresh_token);
       router.push(redirect);
@@ -67,7 +71,7 @@ export function LoginForm() {
     } finally {
       setGoogleLoading(false);
     }
-  }, [redirect, router, notify, t]);
+  }, [redirect, router, notify, t, queryClient]);
 
   const handleGoogleError = useCallback(() => {
     notify({