refactor(server): 移除鉴权并归档遗留路由至 legacy/

- 删除 auth.py 与 deps.py，各路由去除 get_current_user 依赖
- collection.py 更名为 materials.py，冻结链路（ozon/publish/shops/categories）移入 legacy/
- 扩展默认生图服务端口并入 8800 并自动迁移旧配置，水印默认文案改为 Panda Store
- 新增 docs/v2.1/backend-structure.md 后端结构盘点文档

server/api/fx.py

@@ -1,14 +1,13 @@
 """汇率路由。"""
 from __future__ import annotations
 
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter
 
-from deps import get_current_user
 from services.fx import get_fx_rate
 
 router = APIRouter(prefix="/api/fx", tags=["fx"])
 
 
 @router.get("")
-async def fx(_user: dict = Depends(get_current_user)):
+async def fx():
     return await get_fx_rate()