chore: 일별 롤링 로그 추가 (/opt/sb-backend/logs/app.YYYY-MM-DD.log, 30일 보관)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/resources/application.yml

@@ -81,6 +81,12 @@ app:
 
 # ===== Logging =====
 logging:
+  file:
+    name: /opt/sb-backend/logs/app.log
+  logback:
+    rollingpolicy:
+      file-name-pattern: /opt/sb-backend/logs/app.%d{yyyy-MM-dd}.log
+      max-history: 30
   level:
     root: INFO
     com.sb.web: DEBUG