Add a pop-up that happens 7 days after sign-up to "Subscribe to Community"

D.Buzz 2.0 had this pop-up, and even though it's less important for OUR frontend now, we should add a popup that pops up after 7 days of sign-up and repeats every 30 days until they sign-up 👍

No files or tests are named. Start by locating the sign-up date handling and any existing subscription pop-up in the frontend, then verify how a seven-day delay and recurring 30-day display can be represented. Done means the pop-up appears seven days after sign-up and repeats every 30 days until the user subscribes.

Written by the indexing model from the issue text.