Fix Vercel serverless deployment: optimize for fast loading

- Convert Express app to Vercel serverless function
- Add missing /api/files/public endpoint
- Optimize static file routing with proper caching
- Remove unnecessary dependencies for faster cold starts
- Add comprehensive debugging and error handling
- Improve API response times and user experience

api-client.js

@@ -5,20 +5,31 @@ const API_BASE_URL = '';
 
 // API 요청 헬퍼 함수
 async function apiRequest(url, options = {}) {
-    const response = await fetch(`${API_BASE_URL}${url}`, {
-        headers: {
-            'Content-Type': 'application/json',
-            ...options.headers
-        },
-        ...options
-    });
+    console.log(`🔗 API 요청: ${url}`);
+    
+    try {
+        const response = await fetch(`${API_BASE_URL}${url}`, {
+            headers: {
+                'Content-Type': 'application/json',
+                ...options.headers
+            },
+            timeout: 10000, // 10초 타임아웃
+            ...options
+        });
 
-    if (!response.ok) {
-        const error = await response.text();
-        throw new Error(`API Error: ${response.status} - ${error}`);
+        console.log(`📡 응답 상태: ${response.status} ${response.statusText}`);
+
+        if (!response.ok) {
+            const error = await response.text();
+            console.error(`❌ API 오류: ${response.status} - ${error}`);
+            throw new Error(`API Error: ${response.status} - ${error}`);
+        }
+
+        return response;
+    } catch (error) {
+        console.error(`🚨 네트워크 오류:`, error);
+        throw error;
     }
-
-    return response;
 }
 
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