Fix: buy links wallet first; achievement milestones use live buyerCount

- Buying now ensures the wallet is LINKED to the account before the purchase
  (one signature if not linked). Without it, a wallet only connected for the
  faucet bought successfully but credits resolved against member id 0 and never
  showed until a manual link. Matches the "buying links your wallet" promise.
- Dashboard computed achievement milestones from buyerCount BEFORE reading it
  from chain (always 0), so Surge/Circuit/Nexus never unlocked even when
  qualification advanced. Moved the milestone block after the chain read.

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

public/assets/my.js

@@ -1063,6 +1063,14 @@
       wrap.querySelectorAll('button[data-id]').forEach(b => b.addEventListener('click', async () => {
         try {
           b.disabled = true;
+          // the buyer's credits are read by the member id of their LINKED wallet.
+          // If they only connected a wallet (e.g. for the faucet) but never linked
+          // it, link it first (one signature) so the purchase's credits show up.
+          const meNow = await (await fetch('/api/me')).json();
+          if (!meNow.address) {
+            IAP.status('Link your wallet first — one quick signature…');
+            await IAPWallet.signIn();
+          }
           const spNow = await (await fetch('/api/sponsor')).json();
           IAP.status('Confirm the purchase in your wallet…');
           const r = await IAPWallet.buy(Number(b.dataset.id), spNow.sponsorId || 0, b.dataset.cost);