Ship logo (header + favicon) + bolder downline level labels

- Logo lockup (mint lightning/arrow icon + InstantAdPay wordmark) replaces the
  text wordmark in the back-office sidebar and public nav; icon added as the
  favicon on every page. Assets: /logo.png, /logo-icon.png.
- Downline level captions (LEVEL 1 / LEVEL 2 …) are now a bold mint pill instead
  of faint grey — far more readable.

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

public/assets/site.css

@@ -400,7 +400,8 @@ textarea{resize:vertical;font:inherit}
   padding:24px;max-width:520px;width:100%;box-shadow:0 20px 60px rgba(0,0,0,.5)}
 /* ── downline lineage list ── */
 .lin-lvl{margin:10px 0}
-.lin-lvl>.cap{font-size:11px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted);margin-bottom:6px}
+.lin-lvl>.cap{display:inline-block;font-size:13px;font-weight:800;text-transform:uppercase;letter-spacing:.06em;
+  color:var(--mint);background:var(--mint-soft);border:1px solid var(--line-strong);border-radius:8px;padding:4px 10px;margin-bottom:10px}
 .lin-row{display:grid;grid-template-columns:minmax(110px,1.2fr) minmax(0,2fr) auto auto;gap:6px 14px;
   align-items:center;padding:9px 0;border-bottom:1px solid var(--line)}
 .lin-row .nm{font-weight:700;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}