feat(invite): 邀请奖励金账户(与金币隔离) + 比价发奖 + 奖励金提现

- 新增邀请奖励金独立账本: coin_account 加余额列 + invite_cash_transaction 流水表, 与金币现金物理隔离
- bind 改 v2: 绑定只发被邀请人新人金币; 邀请人改在好友首次成功比价时发 2 元奖励金(幂等只发一次)
- 提现链路按 source 分流: 扣款/退款/对账/分页各认账户, 两本账不串
- /invite/me 返回奖励金余额/累计提现/7天倒计时
- 新增 migration(建表加列) + 比价发奖与提现隔离测试

app/api/v1/invite.py

@@ -84,6 +84,8 @@ def _parse_device_model(ua: str) -> str:
 def my_invite(user: CurrentUser, db: DbSession) -> InviteInfoOut:
     code = invite_repo.ensure_code(db, user)
     invited, coins = invite_repo.get_stats(db, user.id)
+    reward_balance, reward_withdrawn = invite_repo.get_reward_stats(db, user.id)
+    days_left, is_fresh_round, countdown_text = invite_repo.compute_invite_countdown(user.created_at)
     sep = "&" if "?" in settings.INVITE_LANDING_URL else "?"
     share_url = f"{settings.INVITE_LANDING_URL}{sep}ref={code}"
     return InviteInfoOut(
@@ -91,6 +93,11 @@ def my_invite(user: CurrentUser, db: DbSession) -> InviteInfoOut:
         share_url=share_url,
         invited_count=invited,
         coins_earned=coins,
+        reward_balance_cents=reward_balance,
+        reward_withdrawn_cents=reward_withdrawn,
+        countdown_days_left=days_left,
+        countdown_is_fresh_round=is_fresh_round,
+        countdown_text=countdown_text,
     )