로그 포맷 통일, slog 적용

frontend/nginx.conf

@@ -1,5 +1,29 @@
+# Map ISO8601 time to "YYYY-MM-DD HH:mm:ss" format
+map $time_iso8601 $time_custom {
+    "~^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2})" "$1-$2-$3 $4:$5:$6";
+}
+
+# Custom JSON Log Format matching Go slog
+log_format json_combined escape=json
+    '{'
+    '"time":"$time_custom",'
+    '"level":"INFO",'
+    '"msg":"http_access",'
+    '"svc":"baron-frontend",'
+    '"status":$status,'
+    '"method":"$request_method",'
+    '"path":"$request_uri",'
+    '"latency":"${request_time}s",'
+    '"ip":"$remote_addr",'
+    '"forwarded_for":"$http_x_forwarded_for",'
+    '"user_agent":"$http_user_agent"'
+    '}';
+
 server {
     listen 5000;
+    include /etc/nginx/mime.types;
+    
+    access_log /var/log/nginx/access.log json_combined;
 
     # Backend API Proxy
     location /api {