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/controller/api/AttachmentController.java

@@ -26,13 +26,14 @@ public class AttachmentController {
 
     private final AttachmentService attachmentService;
 
-    /** 上传（multipart：file 必填；articleId 可空） */
+    /** 上传（multipart：file 必填；articleId 可空；scene 可空 banner/link/site，B2 初步标记） */
     @PostMapping("/upload")
     public AttachmentVo upload(BoaUser authUserWithDept,
                                @RequestParam("siteId") Integer siteId,
                                @RequestParam(value = "articleId", required = false) Integer articleId,
+                               @RequestParam(value = "scene", required = false) String scene,
                                @RequestParam("file") MultipartFile file) {
-        return attachmentService.upload(authUserWithDept, siteId, articleId, file);
+        return attachmentService.upload(authUserWithDept, siteId, articleId, scene, file);
     }
 
     /** 附件列表（orphanOnly=true 仅孤儿） */