Wall ownership ladder: positions 2 and 3 become the member's own at 2 / 5 qualifying buyers

- accounts.wall_offers (JSON, up to 2 offers: label, https link, banner) set from
  Profile > Your wall; upload supported; locks show the buyer threshold.
- /api/wall assembles: position 1 = own line banner; positions 2-3 = own offer
  when unlocked and set, else upline banners (only uplines with a live banner),
  else house ads. Response carries unlocked + buyerCount; wall labels show
  "this wall" / "their line" / "InstantAdPay".
- Chatbot canned answer + facts, follow-up email 7 mention the ladder.

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

public/assets/site.css

@@ -610,3 +610,8 @@ img{max-width:100%}
 
 .lin-row .earn{font-family:var(--mono);font-size:12px;color:var(--muted);white-space:nowrap;font-variant-numeric:tabular-nums}
 .lin-row .earn.on{color:var(--mint);font-weight:700}
+
+.wo-slot{border:1px solid var(--line);border-radius:12px;padding:12px 14px}
+.wo-slot.locked{opacity:.6}
+.wo-head{display:flex;justify-content:space-between;align-items:center;margin-bottom:6px}
+.wo-slot img{max-width:100%;border-radius:8px}