feat: add user medal selection and display

backend/src/main/java/com/openisle/dto/AuthorDto.java

@@ -1,6 +1,7 @@
 package com.openisle.dto;
 
 import lombok.Data;
+import com.openisle.model.MedalType;
 
 /**
  * DTO representing a post or comment author.
@@ -10,5 +11,6 @@ public class AuthorDto {
     private Long id;
     private String username;
     private String avatar;
+    private MedalType displayMedal;
 }
 

backend/src/main/java/com/openisle/dto/MedalDto.java

@@ -10,4 +10,5 @@ public class MedalDto {
     private String description;
     private MedalType type;
     private boolean completed;
+    private boolean selected;
 }

backend/src/main/java/com/openisle/dto/MedalSelectRequest.java

@@ -0,0 +1,9 @@
+package com.openisle.dto;
+
+import com.openisle.model.MedalType;
+import lombok.Data;
+
+@Data
+public class MedalSelectRequest {
+    private MedalType type;
+}