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/binding.py

@@ -0,0 +1,45 @@
+from collections.abc import Mapping
+from datetime import datetime
+from typing import Optional
+
+from app.dao.binding import BindingDAO
+
+
+class BindingService:
+    def __init__(self, db):
+        self.dao = BindingDAO(db)
+
+    def start_bind(self, user_id: int, device_id: str, child_id: int) -> tuple[str, datetime]:
+        bind_token = self.dao.start_bind(user_id, device_id, child_id)
+        return bind_token, datetime.utcnow()
+
+    def confirm_bind(self, bind_token: str, user_id: int) -> Mapping:
+        session = self.dao.get_session(bind_token, user_id)
+        if not session:
+            raise ValueError("Bind session not found")
+        if datetime.utcnow() > session["expires_at"]:
+            raise ValueError("Bind session expired")
+        if session["status"] != 1:
+            raise ValueError("Bind session already processed")
+
+        self.dao.confirm_bind(session["id"], session["device_id"], session["target_child_id"], user_id)
+        return {"device_id": session["device_id"], "child_id": session["target_child_id"]}
+
+    def get_binding(self, device_id: str, user_id: int) -> Optional[Mapping]:
+        return self.dao.get_by_device(device_id, user_id)
+
+    def get_current_binding(self, user_id: int) -> Optional[Mapping]:
+        return self.dao.get_current_by_user(user_id)
+
+    def direct_bind(self, device_id: str, child_id: int, user_id: int) -> Mapping:
+        self.dao.direct_bind(device_id, child_id, user_id)
+        return {"device_id": device_id, "child_id": child_id}
+
+    def unbind(self, device_id: str, user_id: int) -> bool:
+        return self.dao.unbind(device_id, user_id)
+
+    def list_history(self, device_id: str, limit: int = 20, cursor: datetime = None) -> tuple[list, bool]:
+        rows = self.dao.list_history(device_id, limit, cursor)
+        has_more = len(rows) > limit
+        rows = rows[:limit]
+        return rows, has_more