Membership store-credit perks now apply on every renewal, not just at sign-up

Each successful paid renewal on a membership tier with an active store-credit perk now triggers its own store-credit grant, at the perk's current amount. Previously, members on a perk tier were only ever credited once, at sign-up; from their second paid period onward, the perk amount was never applied again, even though the tier still carried it.

A multi-month prepaid renewal schedules the full set of monthly credits it covers, with the first one applied immediately and the rest scheduled to follow, the same way the sign-up credit already worked. If a renewal payment fails, no credit is issued for it; a later successful retry still credits correctly, and a duplicated success notification from Shopify only ever credits once.

This fix applies going forward from its release; it does not retroactively credit renewals that were already billed before the fix was live, so a member's missed renewal credits from before this date won't be issued automatically.

This is live now for every membership tier with a store-credit perk.