支持 .env 配置，并完善源头对接文档与测试订单

- 增加 .env.example 与 godotenv 加载，start.sh 自动读环境变量
- 重写发给源头的开放接口对接文档
- 订单页支持创建测试订单（可直接已支付并复制店铺订单号）

frontend/src/api/index.ts

@@ -45,8 +45,13 @@ export const skinApi = {
 export const orderApi = {
   list: (params?: Record<string, unknown>) =>
     request.get('/orders', { params }).then((r) => r.data.data as PageResult<Order>),
-  create: (data: { skin_id: number; buyer_name?: string; remark?: string }) =>
-    request.post('/orders', data).then((r) => r.data.data as Order),
+  create: (data: {
+    skin_id: number
+    buyer_name?: string
+    remark?: string
+    status?: string
+    distributor_id?: number
+  }) => request.post('/orders', data).then((r) => r.data.data as Order),
   updateStatus: (id: number, status: string) =>
     request.patch(`/orders/${id}/status`, { status }).then((r) => r.data.data),
 }