chore: 清理冗余注释，保留字段/业务含义注释

src/main/java/com/guo/learningprogresstracker/config/serializer/LocalDateTimeSerializer.java

@@ -9,8 +9,6 @@ import java.time.LocalDateTime;
 import java.time.format.DateTimeFormatter;
 
 public class LocalDateTimeSerializer extends StdSerializer<LocalDateTime> {
-
-    // 修改为ISO 8601格式，末尾带Z，表示UTC时区
     private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss'Z'");
 
     public LocalDateTimeSerializer() {
@@ -22,7 +20,6 @@ public class LocalDateTimeSerializer extends StdSerializer<LocalDateTime> {
         if (value == null) {
             gen.writeNull();
         } else {
-            // 这里假设LocalDateTime是UTC时间，直接格式化并加Z
             String formattedDate = value.format(formatter);
             gen.writeString(formattedDate);
         }