Update error message

Update error message when signup is not allowed.

src/lib/supabase/config.ts

@@ -82,6 +82,12 @@ export const getSupabaseKey = () => {
   return 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJyb2xlIjoiYW5vbiIsImlzcyI6InN1cGFiYXNlIiwiaWF0IjoxNzQyMDQ4NTEwLCJleHAiOjQ4OTU2NDg1MTB9.BZx5MF-HldDju9r4eFwOVp9_qj6GOdkjaG6VrJAYAIg';
 };
 
+// Supabase 키 유효성 검사
+export const isValidSupabaseKey = () => {
+  const key = getSupabaseKey();
+  return key && !key.includes('your-onpremise-anon-key');
+};
+
 // CORS 프록시 사용 여부 설정
 export const useCorsProxy = (enabled: boolean) => {
   localStorage.setItem('use_cors_proxy', enabled.toString());