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.

app/pages/join.vue

@@ -317,13 +317,17 @@
       <ParchmentInset>
         <h2>How membership works</h2>
         <ul>
-          <li>Full access to the knowledge commons, Slack, and peer support</li>
+          <li>Full access to the knowledge commons, events and workshops, and community</li>
           <li>Free access to all Ghost Guild events</li>
           <li>Equal access for every member, regardless of contribution</li>
           <li>Your circle reflects where you are, not rank</li>
           <li>Pay what you can ($0&ndash;$50+/month, separate from circle)</li>
           <li>Higher contributions create solidarity spots for others</li>
         </ul>
+        <p>
+          Community connection happens in our Slack workspace, joined in monthly
+          onboarding waves &mdash; there may be a short wait after you join.
+        </p>
       </ParchmentInset>
 
       <!-- THREE CIRCLES -->