feat: 게시글 카테고리에 동행, 중고거래 추가

- PostCategory enum에 동행, 중고거래 추가
- post 테이블 category ENUM 컬럼 마이그레이션 (V52)
- 신규 카테고리 게시글 생성 및 카테고리별 조회 필터링 테스트 추가

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: sukangpunch

src/main/java/com/example/solidconnection/community/post/domain/PostCategory.java

@@ -5,7 +5,7 @@
 import java.util.stream.Collectors;
 
 public enum PostCategory {
-    전체, 자유, 질문;
+    전체, 자유, 질문, 동행, 중고거래;
 
     private static final Set<String> NAMES = Arrays.stream(values())
             .map(Enum::name)

src/main/resources/db/migration/V52__add_companion_and_used_trade_to_post_category.sql

@@ -0,0 +1,2 @@
+ALTER TABLE post
+    MODIFY COLUMN category ENUM ('자유', '전체', '질문', '동행', '중고거래') NULL;

src/test/java/com/example/solidconnection/community/post/service/PostCommandServiceTest.java

@@ -38,6 +38,8 @@
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.mock.web.MockMultipartFile;
 import org.springframework.test.context.bean.override.mockito.MockitoBean;
@@ -164,6 +166,22 @@ class 게시글_생성_테스트 {
             );
         }
 
+        @ParameterizedTest
+        @ValueSource(strings = {"자유", "질문", "동행", "중고거래"})
+        @Transactional
+        void 전체를_제외한_카테고리로_게시글을_생성한다(String category) {
+            // given
+            PostCreateRequest request = createPostCreateRequest(category);
+            List<MultipartFile> imageFiles = List.of();
+
+            // when
+            PostCreateResponse response = postCommandService.createPost(user1.getId(), request, imageFiles);
+
+            // then
+            Post savedPost = postRepository.findById(response.id()).orElseThrow();
+            assertThat(savedPost.getCategory()).isEqualTo(PostCategory.valueOf(category));
+        }
+
         @Test
         void 전체_카테고리로_생성하면_예외가_발생한다() {
             // given

src/test/java/com/example/solidconnection/community/post/service/PostQueryServiceTest.java

@@ -135,6 +135,56 @@ void setUp() {
         );
     }
 
+    @Test
+    void 동행_카테고리로_조회시_해당_카테고리의_게시글만_조회한다() {
+        // given
+        Post 동행_게시글 = postFixture.게시글(
+                "동행 제목",
+                "동행 내용",
+                false,
+                PostCategory.동행,
+                boardFixture.자유게시판(),
+                user
+        );
+
+        // when
+        List<PostListResponse> actualResponses = postQueryService.findPostsByCodeAndPostCategoryOrderByCreatedAtDesc(
+                BoardCode.FREE.name(),
+                PostCategory.동행.name(),
+                null
+        );
+
+        // then
+        assertThat(actualResponses)
+                .extracting(PostListResponse::id)
+                .containsExactly(동행_게시글.getId());
+    }
+
+    @Test
+    void 중고거래_카테고리로_조회시_해당_카테고리의_게시글만_조회한다() {
+        // given
+        Post 중고거래_게시글 = postFixture.게시글(
+                "중고거래 제목",
+                "중고거래 내용",
+                false,
+                PostCategory.중고거래,
+                boardFixture.자유게시판(),
+                user
+        );
+
+        // when
+        List<PostListResponse> actualResponses = postQueryService.findPostsByCodeAndPostCategoryOrderByCreatedAtDesc(
+                BoardCode.FREE.name(),
+                PostCategory.중고거래.name(),
+                null
+        );
+
+        // then
+        assertThat(actualResponses)
+                .extracting(PostListResponse::id)
+                .containsExactly(중고거래_게시글.getId());
+    }
+
     @Test
     void 전체_카테고리로_조회시_해당_게시판의_모든_게시글을_조회한다() {
         // given