feat(invite): 好友邀请后端(注册即生效,邀请人+被邀请人各发1万金币)

- user.invite_code 列 + invite_relation 表(invitee_user_id 唯一 = 幂等防重复发奖)
- GET /api/v1/invite/me(我的码+分享链接+战绩)、POST /api/v1/invite/bind
- 复用 wallet.grant_coins 同事务发币;自邀屏蔽 / 无效码 / 新用户闸(注册72h内才发)
- alembic 迁移(11a1d08c6f55 -> invite_code_and_relation)+ 8 个测试(钱路/幂等/并发兜底全覆盖)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/models/__init__.py

@@ -8,6 +8,7 @@ from app.models.app_config import AppConfig  # noqa: F401
 from app.models.comparison import ComparisonRecord  # noqa: F401
 from app.models.comparison_milestone import ComparisonMilestoneClaim  # noqa: F401
 from app.models.feedback import Feedback  # noqa: F401
+from app.models.invite import InviteRelation  # noqa: F401
 from app.models.meituan_coupon import MeituanCoupon  # noqa: F401
 from app.models.ops_marquee_seed import OpsMarqueeSeed  # noqa: F401
 from app.models.ops_stat_config import OpsStatConfig  # noqa: F401