新增小程序后端代码，包括数据库、路由、服务层等。

小程序前后端打通，包括登录、注册、绑定设备、查询绑定信息，修改小朋友名称等功能。

mini-program/app/service/parent.py

@@ -0,0 +1,33 @@
+from collections.abc import Mapping
+from typing import Optional
+
+from app.dao.parent import ParentDAO
+from app.service import get_db_session
+
+
+class ParentService:
+    def __init__(self, db):
+        self.dao = ParentDAO(db)
+
+    def create(
+        self,
+        openid: str,
+        unionid: Optional[str] = None,
+        nickname: Optional[str] = None,
+        avatar_url: Optional[str] = None,
+    ) -> Mapping:
+        user_id = self.dao.upsert(openid, unionid, nickname, avatar_url)
+        return self.dao.get_by_id(user_id)
+
+    def get(self, user_id: int) -> Optional[Mapping]:
+        return self.dao.get_by_id(user_id)
+
+    def update(
+        self,
+        user_id: int,
+        nickname: Optional[str] = None,
+        avatar_url: Optional[str] = None,
+        phone: Optional[str] = None,
+    ) -> Mapping:
+        self.dao.update(user_id, nickname, avatar_url, phone)
+        return self.dao.get_by_id(user_id)