Ad engine v1: banner/text/login campaigns against on-chain credits

Spec 8b types 1-3. Spend accrues per campaign in batches; burns queue for
the engine signer (admin runs consume() on-chain, /api/admin/burns). Rates
are volume config (adrates.json), rehearsal placeholders until Marty sets
the real card. Public slots serve on the ledger page; campaign manager in
the members area.

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

public/assets/common.js

@@ -84,5 +84,22 @@ window.IAP = (function () {
       + '<span class="tx"><a target="_blank" rel="noopener" href="' + c.explorer + '/tx/' + ev.tx + '">verify ↗</a></span>';
     return div;
   }
-  return { getConfig, fmtPol, fmtUsd, status, renderNav, refreshNavWallet, describeEvent, feedRow, $ };
+  // Render one served ad into #<elId>. Silent if no inventory.
+  async function adSlot(type, elId) {
+    try {
+      const { ad } = await (await fetch('/api/ads/slot?type=' + type)).json();
+      const el = $(elId);
+      if (!ad || !el) return;
+      if (ad.imageUrl) {
+        el.innerHTML = '<a href="' + ad.targetUrl + '" target="_blank" rel="noopener nofollow">'
+          + '<img src="' + ad.imageUrl + '" alt="advertisement" style="max-width:100%;border-radius:8px"></a>'
+          + '<div class="small muted">member ad</div>';
+      } else {
+        el.innerHTML = '<a href="' + ad.targetUrl + '" target="_blank" rel="noopener nofollow"><b>' + ad.title + '</b>'
+          + (ad.body ? ' · ' + ad.body : '') + '</a> <span class="small muted">member ad</span>';
+      }
+      el.hidden = false;
+    } catch (e) {}
+  }
+  return { getConfig, fmtPol, fmtUsd, status, renderNav, refreshNavWallet, describeEvent, feedRow, adSlot, $ };
 })();