feat: 支持先绑定设备后关联儿童档案

- 绑定模型新增 owner_user_id，支持 child_id 为空\n- 新增绑定后设置儿童接口 /bindings/{device_id}/child\n- 前端绑定页改为先绑设备后补充儿童\n- 补充数据库迁移脚本与 DAO 测试用例

banban-mini/src/services/binding.ts

@@ -2,7 +2,7 @@ import { request } from './api'
 
 export interface Binding {
   device_id: string
-  child_id: number
+  child_id: number | null
   status: number
   bound_at: string
 }
@@ -14,7 +14,7 @@ export interface BindStartResponse {
 
 export interface BindHistoryItem {
   device_id: string
-  child_id: number
+  child_id: number | null
   bound_at: string
   unbound_at?: string
 }
@@ -40,7 +40,7 @@ export async function getCurrentBinding(): Promise<Binding | null> {
 // 开始绑定设备
 export async function startBind(data: {
   device_id: string
-  child_id: number
+  child_id?: number
 }): Promise<BindStartResponse> {
   return request<BindStartResponse>('/bindings/start', {
     method: 'POST',
@@ -52,7 +52,7 @@ export async function startBind(data: {
 export async function confirmBind(data: {
   bind_token: string
   challenge_code: string
-}): Promise<{ device_id: string; child_id: number }> {
+}): Promise<{ device_id: string; child_id: number | null }> {
   return request('/bindings/confirm', {
     method: 'POST',
     data,
@@ -83,14 +83,25 @@ export async function unbindDevice(deviceId: string): Promise<void> {
 // 直接绑定设备（手动输入设备码）
 export async function directBind(data: {
   device_id: string
-  child_id: number
-}): Promise<{ device_id: string; child_id: number }> {
+  child_id?: number
+}): Promise<{ device_id: string; child_id: number | null }> {
   return request('/bindings/direct', {
     method: 'POST',
     data,
   })
 }
 
+// Bind child profile after device has been bound to parent account.
+export async function setBindingChild(
+  deviceId: string,
+  data: { child_id: number }
+): Promise<{ device_id: string; child_id: number | null }> {
+  return request(`/bindings/${deviceId}/child`, {
+    method: 'PATCH',
+    data,
+  })
+}
+
 // 获取绑定历史
 export async function getBindHistory(
   deviceId: string,
@@ -102,4 +113,4 @@ export async function getBindHistory(
   params.append('limit', String(limit))
   
   return request<BindHistoryResponse>(`/bindings/history/${deviceId}?${params.toString()}`)
-}
+}