Investigate CORS proxy failure

The CORS proxy is failing despite being enabled, resulting in REST API and database connection errors. Investigate the cause of the failure.

src/lib/supabase/tests.ts

@@ -42,7 +42,11 @@ export const testSupabaseConnection = async () => {
     // 1. REST API 접근 테스트
     try {
       console.log('REST API 테스트 시작...');
-      const apiUrl = `${results.proxyUrl}/rest/v1/`;
+      // 정확한 REST API 엔드포인트 구성
+      const apiUrl = results.proxyUrl.endsWith('/') 
+        ? `${results.proxyUrl}rest/v1/`
+        : `${results.proxyUrl}/rest/v1/`;
+      
       console.log('REST API 테스트 URL:', apiUrl);
       
       const response = await fetch(apiUrl, {