Admin portal (/admin) + free house ads; POL amounts show two decimals

- /admin: email magic-code sign-in allowlisted to ADMIN_EMAIL, 12h admin
  session (cookie iap.adm, persisted in the volume). Bearer ADMIN_PASSWORD
  API access still works. Member area shows an Admin link for that email.
- House ads: admin places banner/text/login/solo/video/featured/visits
  campaigns owned by house@instantadpay.com that cost nothing; budget is
  only a delivery cap, spend is never charged or burned.
- Admin APIs: overview, all campaigns (+pause/resume any), members
  (+re-point sponsor), reports (+resolve), pending burns, rates/site
  config get+patch, creative upload.
- fmtPol rounds to two decimals everywhere (dashboard, toasts, prices).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

public/assets/my.js

@@ -471,6 +471,7 @@
     $('authArea').hidden = !!signedIn;
     $('memberArea').hidden = !signedIn;
     if (!signedIn) return;
+    if ($('adminLink')) $('adminLink').hidden = !me.isAdmin; // admin portal link, only for ADMIN_EMAIL
     setPane(location.hash.slice(1) || 'overview');
     $('campGate').hidden = !!me.memberId;
     $('earnGate').hidden = !!me.memberId;