Put the price on each Buy button to prevent wrong-package buys

Testers were tapping the highlighted "Most Popular" $50 tile's Buy thinking it
was a general buy, and getting a $50 charge they couldn't afford. Each tile
already buys its own package; label the button "Buy $20" etc. so it's
unambiguous which package a tap purchases.

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

public/assets/my.js

@@ -1214,7 +1214,7 @@
           + '<div class="bonus">' + (bonus > 0 ? '+' + bonus.toLocaleString() + ' bonus credits' : '&nbsp;') + '</div>'
           + '<div class="pol">' + (p.costWei ? IAP.fmtPol(p.costWei) + ' POL right now' : 'paused') + '</div>'
           + '<button class="btn small" data-id="' + p.id + '" data-cost="' + (p.costWei || '') + '"'
-          + (p.costWei ? '' : ' disabled') + '>Buy</button>';
+          + (p.costWei ? '' : ' disabled') + '>Buy $' + Math.round(p.priceCents / 100) + '</button>';
         wrap.appendChild(div);
       }
       wrap.querySelectorAll('button[data-id]').forEach(b => b.addEventListener('click', async () => {