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/SiteService.java

@@ -40,6 +40,14 @@ public class SiteService {
     private final ApplicationEventPublisher eventPublisher;
     private final com.yunhai.cms.theme.ThemeRegistry themeRegistry;
 
+    /**
+     * B2 附件引用：站点配置 logo/favicon 回写场景引用。
+     * 字段注入 + @Lazy 打破与 AttachmentService 的构造器循环依赖（AttachmentService → SiteService）。
+     */
+    @org.springframework.beans.factory.annotation.Autowired
+    @org.springframework.context.annotation.Lazy
+    private AttachmentService attachmentService;
+
     /** config_json 已知键约束（与前端 utils/siteConfigForm.ts 保持一致，docs/09 §0 键清单） */
     private static final ObjectMapper CONFIG_MAPPER = new ObjectMapper();
     private static final Pattern HOST_PATTERN = Pattern.compile(
@@ -140,6 +148,8 @@ public class SiteService {
         site.setConfigJson(mergeThemeParams(req, resolvedTheme));
         site.setStatus(req.getStatus() == null ? 1 : req.getStatus());
         site = siteRepository.save(site);
+        // B2 附件引用：config_json 的 logo/favicon 指向上传文件时回写场景引用（换图/清空自动解引用旧值）
+        attachmentService.markSiteConfigUsed(site.getId(), ExtJsonUtils.parse(site.getConfigJson()));
         eventPublisher.publishEvent(new SiteContentChangedEvent(site.getId(), "site"));
         return SiteVo.of(site);
     }