fix(launch-flow): align Slack-wait copy across join, dashboard, welcome email

- /join "How membership works" lists community (not Slack) as a benefit;
  adds a note that Slack invitations come in monthly onboarding waves.
- Dashboard slack-coming note drops "2–3 weeks" timeline; uses the same
  monthly-waves phrasing.
- Welcome email no longer points new members to Slack (which they don't
  yet have access to); directs them to reply instead.

server/utils/resend.js

@@ -282,7 +282,7 @@ Welcome to Ghost Guild! You're now part of the ${member.circle} circle.
 Sign in to your dashboard to get started:
 ${baseUrl}/member/dashboard
 
-If you have questions, reach out to jennie + eileen on Slack or reply to this email.`,
+If you have questions, just reply to this email.`,
     });
 
     if (error) {