Wall page: mint QR, achievement badge, admin-ad backfill, join gated on views

- QR is mint-green (still high-contrast for reliable scanning).
- The wall shows the owner's achievement badge next to their avatar.
- Positions 2 & 3 fill with upline line-banners, then ADMIN ADS when there's no
  upline (configurable via data/admin-wall-ads.json; sensible default) so the
  wall is never sparse.
- "Join free through this wall" is disabled until the visitor has viewed every
  ad on the wall, with a "X/Y viewed" prompt.

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

public/shorts.html

@@ -4,7 +4,7 @@
 <meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1">
 <title>Shorts | InstantAdPay</title>
 <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Sora:wght@600;700;800&display=swap">
-<link rel="stylesheet" href="/assets/site.css?v=20260906m">
+<link rel="stylesheet" href="/assets/site.css?v=20260907s">
 <style>
   html,body{height:100%;margin:0;overflow:hidden;background:#000}
   .sh{position:fixed;inset:0;display:flex;flex-direction:column;background:#000;color:var(--ink,#e8fff7)}