Featured to top, centered, capped; banner ads capped 728px centered; slot CTA

- Featured card moved to the top of Overview, centered, max 760px; the rotating
  link is capped to 728px and centered (banner-sized, not a huge block).
- Served banner creatives cap at min(100%,728px), centered — kills the oversized
  sample banner; ad slots center their creative + label.
- Featured self-sell: shows "N of C slots open today" + "Feature your link →"
  that jumps to Campaigns with Featured preselected.
- Campaign target/image/video URL fields get autocomplete=off and clear when the
  Campaigns pane opens, so no residual (e.g. massifly) URL carries over.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/assets/common.js

@@ -117,8 +117,9 @@ window.IAP = (function () {
       const el = $(elId);
       if (!ad || !el) return;
       if (ad.imageUrl) {
+        el.style.textAlign = 'center';
         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>'
+          + '<img src="' + ad.imageUrl + '" alt="advertisement" style="max-width:min(100%,728px);height:auto;display:block;margin:0 auto;border-radius:8px"></a>'
           + '<div class="small muted">member ad' + reportTag(ad) + '</div>';
       } else {
         el.innerHTML = '<a href="' + ad.targetUrl + '" target="_blank" rel="noopener nofollow"><b>' + ad.title + '</b>'