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/routers/wechat_auth.py

@@ -0,0 +1,87 @@
+import logging
+from typing import Optional
+
+from fastapi import APIRouter, Depends, HTTPException, Request, status
+from pydantic import BaseModel
+from sqlalchemy import text
+from sqlalchemy.orm import Session
+
+try:
+    from app.db import get_db
+    from app.security import create_access_token
+except ModuleNotFoundError:
+    from db import get_db
+    from security import create_access_token
+
+
+router = APIRouter(prefix="/auth", tags=["auth"])
+logger = logging.getLogger("app.auth")
+
+
+class LoginRequest(BaseModel):
+    username: Optional[str] = None
+    password: Optional[str] = None
+    code: Optional[str] = None
+    nickname: Optional[str] = None
+    avatar_url: Optional[str] = None
+
+
+class LoginResponse(BaseModel):
+    access_token: str
+    expires_in: int
+    user_id: int
+
+
+@router.post("/login", response_model=LoginResponse)
+def login(
+    payload: LoginRequest,
+    request: Request,
+    db: Session = Depends(get_db),
+) -> LoginResponse:
+    logger.info(f"/auth/login called with code={payload.code[:20] if payload.code else None}...")
+    identifier = payload.code or payload.username
+    if not identifier:
+        raise HTTPException(status_code=400, detail="username or code is required")
+
+    with db.begin():
+        row = (
+            db.execute(
+                text("SELECT user_id FROM parents WHERE openid = :openid"),
+                {"openid": identifier},
+            ).mappings().first()
+        )
+
+        if row:
+            user_id = int(row["user_id"])
+            logger.info(f"Existing user found: user_id={user_id}")
+            if payload.nickname or payload.avatar_url:
+                db.execute(
+                    text(
+                        """
+                        UPDATE parents
+                        SET nickname = COALESCE(:nickname, nickname),
+                            avatar_url = COALESCE(:avatar_url, avatar_url)
+                        WHERE user_id = :user_id
+                        """
+                    ),
+                    {"user_id": user_id, "nickname": payload.nickname, "avatar_url": payload.avatar_url},
+                )
+        else:
+            logger.info("Creating new user...")
+            db.execute(
+                text(
+                    "INSERT INTO parents (openid, nickname, avatar_url, status) VALUES (:openid, :nickname, :avatar_url, 1)"
+                ),
+                {"openid": identifier, "nickname": payload.nickname, "avatar_url": payload.avatar_url},
+            )
+            user_id = int(db.execute(text("SELECT last_insert_rowid()")).scalar_one())
+            logger.info(f"New user created: user_id={user_id}")
+
+    access_token, expires_in = create_access_token(user_id=user_id)
+    logger.info(f"Login succeeded: user_id={user_id}, expires_in={expires_in}")
+    return LoginResponse(access_token=access_token, expires_in=expires_in, user_id=user_id)
+
+
+@router.post("/logout")
+def logout(request: Request):
+    return {"message": "logged out"}