feat: 更新认证逻辑，支持通过openid查找或创建用户，并调整JWT负载字段

backend/app/routers/auth.py

@@ -31,13 +31,14 @@ class TokenResponse(BaseModel):
 
 
 def _build_token(user: User) -> str:
-    """生成自包含 JWT：sub + openid + mobile"""
+    """生成自包含 JWT：uid + openid + phone（兼容外部 token 格式）"""
     expire = datetime.now(timezone.utc) + timedelta(days=30)
     payload = {
-        "sub": str(user.id),
+        "uid": str(user.id),
         "openid": user.openid,
-        "mobile": user.phone or "",
+        "phone": user.phone or "",
         "exp": expire,
+        "iss": "localhost",
     }
     return jwt.encode(payload, settings.jwt_secret_key, algorithm=settings.jwt_algorithm)