feat: 카테고리 목록 반환 API (#49)

- 카테고리 목록 반환 API 생성
- 클라이언트와 주고받는 카테고리명 한글로 수정

src/main/java/com/gamsa/activity/constant/Category.java

@@ -1,5 +1,7 @@
 package com.gamsa.activity.constant;
 
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonValue;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 
@@ -15,4 +17,28 @@ public enum Category {
     OTHER_ACTIVITIES("기타 활동");
 
     private final String name;
+
+    @JsonCreator
+    public static Category fromValues(String value) {
+        for (Category category : Category.values()) {
+            if (category.getName().equals(value)) {
+                return category;
+            }
+        }
+        throw new IllegalArgumentException("Unknown value: " + value);
+    }
+
+    public static Category fromValuesForSlice(String value) {
+        for (Category category : Category.values()) {
+            if (category.getName().equals(value)) {
+                return category;
+            }
+        }
+        return null;    // QueryDSL 에서는 null일 경우 필터링에서 제외하므로 null 반환 허용
+    }
+
+    @JsonValue
+    public String toValue() {
+        return this.name;
+    }
 }

src/main/java/com/gamsa/activity/controller/ActivityController.java

@@ -28,15 +28,15 @@ public class ActivityController {
 
     @GetMapping
     public Slice<ActivityFindSliceResponse> findSlice(
-        @RequestParam(required = false) Category category,
+        @RequestParam(required = false) String category,
         @RequestParam(required = false) Integer sidoGunguCode,
         @RequestParam(required = false) Integer sidoCode,
         @RequestParam(defaultValue = "false") boolean teenPossibleOnly,
         @RequestParam(defaultValue = "false") boolean beforeDeadlineOnly,
         Pageable pageable) {
 
         ActivityFilterRequest request = ActivityFilterRequest.builder()
-            .category(category)
+            .category(Category.fromValuesForSlice(category))
             .sidoGunguCode(sidoGunguCode)
             .sidoCode(sidoCode)
             .teenPossibleOnly(teenPossibleOnly)

src/main/java/com/gamsa/activity/controller/CategoryController.java

@@ -0,0 +1,17 @@
+package com.gamsa.activity.controller;
+
+import com.gamsa.activity.constant.Category;
+import java.util.List;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/api/v1/activities/categories")
+public class CategoryController {
+
+    @GetMapping
+    public List<Category> findAllCategories() {
+        return List.of(Category.values());
+    }
+}