refactor(server): 移除已放弃的 Ozon API 直传模块，新增素材删除接口

- 删除 shops/publish/categories/ozon 相关路由、模型、schema 与客户端服务（V2.1 决策放弃 API 直传，改人工上传）
- materials 新增 DELETE /assets/{id}：删除素材记录与本地文件，并同步修正 asset_counts
- 试算页支持单张素材删除，生图弹窗交互微调
- 新增 docs/v2.1/HANDOFF.md 工作交接说明，README 补充索引

server/api/suite.py

@@ -35,7 +35,7 @@ from services.planner import generate_plan
 from services.prompts import build_context, build_prompt, type_name
 from services.storage import download_bytes, get_storage, local_path
 from services.suite_service import append_generated_asset, texts_to_raw, validate_model
-from services.tasks import IMG_OK, create_task, get_task
+from services.tasks import IMG_OK, TaskImage, create_task, get_task
 
 router = APIRouter(prefix="/api", tags=["suite"])
 
@@ -246,6 +246,7 @@ async def suite_image_edit(req: ImageEditSingleRequest) -> ImageEditSingleRespon
             asset_id = await append_generated_asset(
                 req.product_id,
                 TaskImage(type_id="custom", name="AI生图", url=url, status="ok"),
+                after_asset_id=req.after_asset_id,
             )
         except Exception:  # noqa: BLE001
             pass  # 回写失败不影响结果返回，图片已在任务网格可见