InstantAdPay banner kit (kie.ai): hero + leaderboard + rectangle in Promo tools

- 3 brand banners generated via kie.ai (mint-on-dark Web3 aesthetic), served from /banners/
- Promo tools Banners card now shows the kit with copy-image-URL

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

public/assets/site.css

@@ -259,6 +259,11 @@ textarea{resize:vertical;font:inherit}
   #boBurger{display:block}
   .bo-content{padding:18px}
 }
+/* ── promo banners ── */
+.promo-banners{display:flex;flex-direction:column;gap:14px;margin-top:12px}
+.pb-item img{max-width:100%;border-radius:8px;border:1px solid var(--line-strong);display:block}
+.pb-item .pb-row{display:flex;gap:10px;align-items:center;margin-top:6px;flex-wrap:wrap}
+.pb-item .pb-size{font-family:var(--mono);font-size:11px;color:var(--muted)}
 /* ── featured day-slot picker ── */
 .feat-days{display:flex;gap:8px;flex-wrap:wrap}
 .feat-day{flex:0 0 auto;min-width:82px;padding:8px 10px;border:1px solid var(--line-strong);border-radius:10px;