feat: implement reading progress tracking with Redis caching and API endpoints

src/main/java/com/magamochi/userinteraction/service/ReadingProgressService.java

@@ -98,12 +98,12 @@ public class ReadingProgressService {
         chapterId);
     return progressRepository
         .findById(new UserReadingProgressId(userId, chapterId))
-        .map(entity -> mapToDto(entity));
+        .map(this::mapToDto);
   }
 
   @Transactional
   public void flushDirtyRecords() {
-    log.info("Starting flush of reading progress from Redis to SQL");
+    log.info("Flushing reading progress from Redis to SQL");
 
     var keys = redisTemplate.keys(REDIS_SEARCH_PATTERN);
     if (isNull(keys) || keys.isEmpty()) {