fix(projects+assets): 项目封面引用真实商品图 + 资产库排除软删资产

- 项目卡封面:废弃「项目名关键词→静态 mock 假图」映射(与真实数据脱节,导致全是假面膜图),
  改用后端 cover_preview_url(取商品 cover_asset 主图);无商品图 → 干净占位
- 资产库 queryset/summary/facets 补 is_deleted=False:软删资产不再出现在资产库与 tab 计数
  (此前 is_deleted 字段在资产库未生效,软删无效)
- 单测 AssetSoftDeleteTests:列表 + 计数均排除软删

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

core/backend/apps/assets/views.py

@@ -79,7 +79,7 @@ class AssetViewSet(TeamScopedViewSetMixin, ModelViewSet):
         """服务端过滤,支持各页按需懒加载(不再前端取全量后客户端切片)。
         参数:tab(资产库分桶)/category/asset_type/source/product/q(搜索)/m_<key>(metadata 过滤)/ordering。
         默认按 -created_at 排序——无 ORDER BY 时分页会重/漏。"""
-        qs = super().get_queryset()
+        qs = super().get_queryset().filter(is_deleted=False)  # 软删资产不出现在资产库
         p = self.request.query_params
         if p.get("tab"):
             qs = qs.filter(_tab_q(p["tab"]))
@@ -109,7 +109,7 @@ class AssetViewSet(TeamScopedViewSetMixin, ModelViewSet):
     @action(detail=False, methods=["get"])
     def summary(self, request):
         """资产库 tab 计数(人物/场景/商品图/成片/我的上传/未分类),供 tab 徽标——不必取全量。"""
-        base = Asset.objects.filter(team=self.get_team())
+        base = Asset.objects.filter(team=self.get_team(), is_deleted=False)
         tabs = ["people", "scenes", "products", "tryon", "kits", "creations", "materials", "uploads", "unclassified"]
         return Response({t: base.filter(_tab_q(t)).count() for t in tabs})
 
@@ -117,7 +117,7 @@ class AssetViewSet(TeamScopedViewSetMixin, ModelViewSet):
     def facets(self, request):
         """某 tab 下真实存在的筛选项(来源/类型/指定 metadata 键的取值),供下拉「只列真有的」。
         参数:tab、meta_keys=gender,age,role,...(逗号分隔)。"""
-        base = Asset.objects.filter(team=self.get_team())
+        base = Asset.objects.filter(team=self.get_team(), is_deleted=False)
         if request.query_params.get("tab"):
             base = base.filter(_tab_q(request.query_params["tab"]))
         sources = sorted(s for s in base.values_list("source", flat=True).distinct() if s)