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

extensions/collector/entrypoints/sidepanel/App.tsx

@@ -141,7 +141,7 @@ const App: React.FC = () => {
   const [settings, setSettings] = useState<BackendSettings>({
     baseUrl: 'http://127.0.0.1:3300',
     token: '',
-    watermark: { enabled: false, type: 'image', text: 'xiongmaoyx', opacity: 30 },
+    watermark: { enabled: false, type: 'image', text: 'Panda Store', opacity: 30 },
     reportEnabled: true,
     reportBaseUrl: 'http://127.0.0.1:8800',
     studioBaseUrl: 'http://localhost:8900',