[Receipts] Add flash message after activating inbox address

<img width="454" height="143" alt="Image" src="https://github.com/user-attachments/assets/af69a70d-2270-4767-aaef-968b7b9b44b7" />

We should have a flash message after the thumbs up is clicked.

https://hackclub.slack.com/archives/C026RKHLPNJ/p1786387118869609?thread_ts=1786386685.504039&cid=C026RKHLPNJ