feat(B2): 附件引用模型-cms_attachment 增 ref_type/ref_id,消灭孤儿误报

- 实体/双 SQL 加列+idx_att_ref;upload 增 scene 白名单(banner/link/site)
- AttachmentService 新增 markUsed/release/markSiteConfigUsed(webUrl 反查,幂等)
- 未使用=articleId 与 refType 均空;page 返回 unusedCount(前后端同步改名无兼容别名)
- Banner/Link 保存先解引用再回写(换图旧图回未使用);Site 配置 logo/favicon 引用回写(@Lazy 解循环依赖)
- 新增13例(Attachment6/Banner3/Link2/Site2)+既有语义断言更新;mvn -o test 全绿

src/main/java/com/yunhai/cms/service/impl/BannerService.java

@@ -34,6 +34,7 @@ public class BannerService {
     private final CmsCategoryRepository categoryRepository;
     private final SiteService siteService;
     private final ApplicationEventPublisher eventPublisher;
+    private final AttachmentService attachmentService;
 
     public List<BannerVo> list(BoaUser user, Integer siteId, String position) {
         siteService.requireManageable(user, siteId);
@@ -81,6 +82,9 @@ public class BannerService {
         }
         banner.setStatus(req.getStatus() == null ? 1 : req.getStatus());
         banner = bannerRepository.save(banner);
+        // B2 附件引用：先解引用再回写新图（编辑换图时旧图回未使用）；幂等
+        attachmentService.release("banner", banner.getId());
+        attachmentService.markUsed(site.getId(), req.getImageUrl(), "banner", banner.getId());
         eventPublisher.publishEvent(new SiteContentChangedEvent(site.getId(), "banner"));
         return BannerVo.of(banner);
     }
@@ -94,6 +98,7 @@ public class BannerService {
             throw new BizException(ErrorCode.FORBIDDEN, "无权删除该轮播");
         }
         bannerRepository.delete(banner);
+        attachmentService.release("banner", banner.getId());
         eventPublisher.publishEvent(new SiteContentChangedEvent(site.getId(), "banner"));
     }