feat: 내 글/댓글 모아보기 API

- GET /board/my/posts, /board/my/comments (페이징)
- PostSummary 에 category 추가, MyCommentResponse(글 제목·카테고리 포함)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/resources/mapper/CommentMapper.xml

@@ -36,6 +36,19 @@
         UPDATE comment SET blocked = #{blocked} WHERE id = #{id}
     </update>
 
+    <select id="findMyPage" resultType="com.sb.web.board.dto.MyCommentResponse">
+        SELECT c.id, c.content, c.created_at, p.id AS post_id, p.title AS post_title, p.category
+        FROM comment c
+        JOIN post p ON p.id = c.post_id
+        WHERE c.author_id = #{memberId}
+        ORDER BY c.id DESC
+        LIMIT #{size} OFFSET #{offset}
+    </select>
+
+    <select id="countMyComments" parameterType="long" resultType="long">
+        SELECT COUNT(*) FROM comment WHERE author_id = #{memberId}
+    </select>
+
     <insert id="insert" parameterType="com.sb.web.board.domain.Comment"
             useGeneratedKeys="true" keyProperty="id">
         INSERT INTO comment (post_id, author_id, author_name, content, created_at)