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/schemas/shop.py

@@ -1,33 +0,0 @@
-"""店铺（Ozon 凭证）请求/响应模型。"""
-from __future__ import annotations
-
-from datetime import datetime
-from uuid import UUID
-
-from pydantic import BaseModel, ConfigDict
-
-
-class ShopCreate(BaseModel):
-    name: str
-    client_id: str
-    api_key: str
-    currency_code: str = "CNY"
-
-
-class ShopUpdate(BaseModel):
-    name: str | None = None
-    client_id: str | None = None
-    api_key: str | None = None
-    currency_code: str | None = None
-
-
-class ShopListItem(BaseModel):
-    model_config = ConfigDict(from_attributes=True)
-
-    id: UUID
-    name: str
-    currency_code: str
-    status: str
-    client_id_masked: str = ""  # 打码尾号
-    last_checked_at: datetime | None = None
-    created_at: datetime

server/schemas/suite.py

@@ -153,6 +153,10 @@ class ImageEditSingleRequest(BaseModel):
     prompt: str = Field(..., min_length=1, description="用户要求（必填，进生图指令）")
     model: str = Field(default="nano-banana-2")
     append: bool = Field(default=True, description="结果是否追加为商品素材（generated 组）")
+    after_asset_id: str | None = Field(
+        default=None,
+        description="插入锚点：新素材排在该素材（generated 组）之后，方便与原图对比；缺省追加到组尾",
+    )
 
 
 class ImageEditSingleResponse(BaseModel):