feat: 初始化孕育无忧全栈项目基础代码结构

完成项目初始搭建，包含后端FastAPI+MongoDB服务、前端React+Vite项目的完整基础结构，添加各类配置文件与依赖清单，涵盖核心业务初始框架。

backend/app/routers/auth.py

@@ -0,0 +1,87 @@
+import uuid
+
+from fastapi import APIRouter, HTTPException
+from pymongo.errors import DuplicateKeyError
+
+from app.models.user import User
+from app.schemas.auth import WechatLoginRequest, PhoneLoginRequest, TokenResponse
+from app.middleware.auth import create_access_token
+from app.services.wechat import code_to_session
+
+router = APIRouter()
+
+
+@router.post("/demo-login", response_model=TokenResponse)
+async def demo_login():
+    """Web 体验用的演示登录，每次创建独立的临时用户"""
+    demo_openid = f"demo_{uuid.uuid4().hex[:12]}"
+    user = User(
+        openid=demo_openid,
+        name="体验用户",
+    )
+    await user.insert()
+
+    token = create_access_token(str(user.id))
+    return TokenResponse(
+        access_token=token,
+        user_id=str(user.id),
+        is_new_user=True,
+    )
+
+
+@router.post("/wechat-login", response_model=TokenResponse)
+async def wechat_login(req: WechatLoginRequest):
+    """微信小程序登录"""
+    try:
+        wechat_data = await code_to_session(req.code)
+    except Exception as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+    openid = wechat_data["openid"]
+    user = await User.find_one(User.openid == openid)
+    is_new = user is None
+
+    if not user:
+        user = User(
+            openid=openid,
+            session_key=wechat_data.get("session_key"),
+            union_id=wechat_data.get("unionid"),
+        )
+        await user.insert()
+    else:
+        user.session_key = wechat_data.get("session_key")
+        await user.save()
+
+    token = create_access_token(str(user.id))
+    return TokenResponse(
+        access_token=token,
+        user_id=str(user.id),
+        is_new_user=is_new,
+    )
+
+
+@router.post("/phone-login", response_model=TokenResponse)
+async def phone_login(req: PhoneLoginRequest):
+    """手机号登录（简化版，生产环境需接入短信验证）"""
+    # TODO: 接入真实短信验证服务
+    if req.sms_code != "123456":
+        raise HTTPException(status_code=400, detail="验证码错误")
+
+    user = await User.find_one(User.phone == req.phone)
+    is_new = user is None
+
+    if not user:
+        try:
+            user = User(openid=f"phone_{req.phone}", phone=req.phone)
+            await user.insert()
+        except DuplicateKeyError:
+            # 并发竞态：另一个请求已创建该用户，回退查找
+            user = await User.find_one(User.phone == req.phone)
+            is_new = False
+
+    token = create_access_token(str(user.id))
+    return TokenResponse(
+        access_token=token,
+        user_id=str(user.id),
+        is_new_user=is_new,
+    )