Legacy bridge pages, welcome-back credits, holding-tank alerts

- /from/faucetwave and /from/tieroneads (?seg=advertiser): the squeeze page with
  brand copy and no video, sponsor cookie cleared so arrivals land in the holding
  tank, angle + a legacy:<brand> source recorded on the account.
- legacy.js: private list DATA_DIR/legacy.json (email -> brand, segment); listed
  emails get a one-time credit grant at account creation (legacyCreditsAdvertiser
  500 / legacyCreditsEarner 150, admin-editable), recorded in legacy-grants.json.
- Holding-tank alerts: dashboard payload carries who is waiting (Overview notice
  with usernames + adopt link), and a 15-minute tick posts new arrivals to the
  shared Telegram payments topic.
- Chatbot prompt lines + admin setting labels.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

public/my.html

@@ -229,6 +229,7 @@
           </div>
           <div class="nc-steps" id="ncSteps"></div>
           <p class="small" id="launchMark" hidden style="margin:10px 0 0"></p>
+          <p class="small" id="tankNotice" hidden style="margin:10px 0 0"></p>
         </div>
         <div class="card" id="lineTreeCard">
           <div class="card-head"><h3>Your line at a glance</h3><span class="sub" id="treeSub"></span></div>