fix(posts): PostgreSQL untyped NULL 파라미터 500 + category_id UPDATE 누락

listPublishedKeyset SQL에서 #{categoryId}/#{cursorCreatedAt} IS NULL 조건 사용 시
PostgreSQL이 바인드 파라미터 타입을 결정하지 못해
PSQLException: could not determine data type of parameter $1 → 500 발생.
파라미터에 ::bigint / ::timestamptz 명시 캐스트 추가로 수정.

update() SQL에서 category_id = #{categoryId} 컬럼 누락 — 카테고리 변경이
DB에 반영되지 않는 데이터 정합성 버그 함께 수정.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K3FeMrbtxfTScjrwUukyHD

src/main/java/com/pandoli365/bibimbap/mapper/PostsMapper.java

@@ -41,10 +41,10 @@ public interface PostsMapper {
             JOIN post_categories c ON c.id = p.category_id
             WHERE p.status = 'PUBLISHED'
               AND p.is_delete = false
-              AND (#{categoryId} IS NULL OR p.category_id = #{categoryId})
+              AND (#{categoryId}::bigint IS NULL OR p.category_id = #{categoryId}::bigint)
               AND (
-                    #{cursorCreatedAt} IS NULL
-                    OR (p.created_at, p.id) < (#{cursorCreatedAt}, #{cursorId})
+                    #{cursorCreatedAt}::timestamptz IS NULL
+                    OR (p.created_at, p.id) < (#{cursorCreatedAt}::timestamptz, #{cursorId}::bigint)
                   )
             ORDER BY p.created_at DESC, p.id DESC
             LIMIT #{limit}
@@ -119,7 +119,8 @@ public interface PostsMapper {
 
     @Update("""
             UPDATE posts
-            SET title = #{title},
+            SET category_id = #{categoryId},
+                title = #{title},
                 body_markdown = #{bodyMarkdown},
                 body_sanitized_html = #{bodySanitizedHtml},
                 link_url = #{linkUrl},