feat(board): 신고 목록 조회 API + 신고 무시(관리자)

- GET /api/board/reports — 글/댓글 신고 대상별 집계(UNION, 신고 많은 순)
- POST /api/board/reports/dismiss — 블라인드 없이 신고 기록만 초기화
- 관리자 신고 관리 화면 백엔드

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

src/main/resources/mapper/ReportMapper.xml

@@ -12,6 +12,29 @@
         SELECT COUNT(*) FROM report WHERE target_type = #{targetType} AND target_id = #{targetId}
     </select>
 
+    <!-- 신고된 글/댓글 목록 (대상별 집계). 신고 많은 순 → 최근 신고 순. -->
+    <select id="listReported" resultType="com.sb.web.board.dto.ReportedItem">
+        SELECT 'POST' AS targetType, r.target_id AS targetId, p.id AS postId,
+               p.category AS category, p.title AS title, LEFT(p.content, 120) AS content,
+               p.author_id AS authorId, p.author_name AS authorName, p.blocked AS blocked,
+               COUNT(*) AS reportCount, MAX(r.created_at) AS lastReportedAt
+        FROM report r
+        JOIN post p ON p.id = r.target_id
+        WHERE r.target_type = 'POST'
+        GROUP BY p.id
+        UNION ALL
+        SELECT 'COMMENT' AS targetType, r.target_id AS targetId, c.post_id AS postId,
+               pp.category AS category, pp.title AS title, LEFT(c.content, 120) AS content,
+               c.author_id AS authorId, c.author_name AS authorName, c.blocked AS blocked,
+               COUNT(*) AS reportCount, MAX(r.created_at) AS lastReportedAt
+        FROM report r
+        JOIN comment c ON c.id = r.target_id
+        JOIN post pp ON pp.id = c.post_id
+        WHERE r.target_type = 'COMMENT'
+        GROUP BY c.id
+        ORDER BY reportCount DESC, lastReportedAt DESC
+    </select>
+
     <delete id="deleteByTarget">
         DELETE FROM report WHERE target_type = #{targetType} AND target_id = #{targetId}
     </delete>