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/models/__init__.py

@@ -0,0 +1,37 @@
+from sqlalchemy.orm import DeclarativeBase
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+from app.models.entities import (
+    Parent,
+    Child,
+    ParentChildRelation,
+    DeviceBinding,
+    DeviceBindSession,
+    DeviceBindHistory,
+    Card,
+    DeviceSetting,
+    IMConversation,
+    IMMessage,
+    ChildLocationCurrent,
+    ChildLocationHistory,
+)
+
+__all__ = [
+    "Base",
+    "Parent",
+    "Child",
+    "ParentChildRelation",
+    "DeviceBinding",
+    "DeviceBindSession",
+    "DeviceBindHistory",
+    "Card",
+    "DeviceSetting",
+    "IMConversation",
+    "IMMessage",
+    "ChildLocationCurrent",
+    "ChildLocationHistory",
+]