refill credits at luanode before expiry
i'm not sure we get a notification (even though we fixed the contact address in #40235 (closed)), so just make sure we don't run out of credit on luanode.
the current dashboard says:
Sum: $8.20 monthly. You have $39.18 credits remaining (estimated credit exhaustion in 143.4 days).
so, let's set a warning in 110 days (~4 months?)