Show deposit progress after the invoice

- The invoice checks the server every 30 seconds and shows the amount
  detected, then the confirmation once the server is listed.
- The server page gets the same banner, with a 24-hour limit on checks.
- The invoice link is now "Follow your payment", so the invoice can be
  closed and the deposit followed from a fixed address.

index.html

@@ -639,7 +639,61 @@ window.addEventListener('popstate', () => {
   fetchMinAmount();
 });
 
+// After an invoice is shown, ask the server page every 30 seconds whether the
+// payment has been seen, so the visitor does not have to reload. The status only
+// moves forward: unconfirmed_balance may go back to 0 before the deposit is
+// credited, and that must not look as if the payment had disappeared.
+const DEPOSIT_POLL_MS = 30000;
+const DEPOSIT_POLL_MAX_MS = 24 * 60 * 60 * 1000;
+let depositWatch = null;
+
+function stopDepositWatch() {
+  if (depositWatch) clearInterval(depositWatch.timer);
+  depositWatch = null;
+}
+
+async function pollDeposit() {
+  const watch = depositWatch;
+  if (!watch) return;
+  if (Date.now() - watch.started > DEPOSIT_POLL_MAX_MS) return stopDepositWatch();
+  let data;
+  try {
+    const response = await fetch(`/weinfodata/${watch.chain}/${watch.id}`);
+    if (!response.ok) return;
+    data = await response.json();
+  } catch (err) {
+    return;  // temporary network problem: try again at the next round
+  }
+  if (watch !== depositWatch || !data) return;
+  const expiry = data.expiry_date || null;
+  // The first answer is the reference: listing or renewal changes the expiry date.
+  if (watch.expiry === undefined) watch.expiry = expiry;
+  const status = document.getElementById('iv-status');
+  const bal = data.balance != null ? fmt(data.balance) : null;
+  const unc = data.unconfirmed_balance != null ? fmt(data.unconfirmed_balance) : null;
+  if (bal) document.getElementById('iv-balance').textContent = unc ? bal + ' (' + unc + ')' : bal;
+  if (expiry && expiry !== watch.expiry) {
+    status.className = 'ok-line';
+    status.textContent = '✓ Payment confirmed: your server is now listed.';
+    stopDepositWatch();
+    fetchData();
+  } else if (Number(data.unconfirmed_balance) > 0 && !watch.detected) {
+    watch.detected = true;
+    status.className = 'ok-line';
+    status.textContent = 'Payment detected: ' + fmt(data.unconfirmed_balance) + ' sats, waiting for 3 confirmations (about 30 minutes). This page updates by itself, or use the "Follow your payment" link below.';
+  }
+}
+
+function startDepositWatch(chain, id) {
+  stopDepositWatch();
+  if (!id) return;
+  depositWatch = { chain, id, started: Date.now(), detected: false, expiry: undefined };
+  depositWatch.timer = setInterval(pollDeposit, DEPOSIT_POLL_MS);
+  pollDeposit();
+}
+
 document.getElementById('submit').addEventListener('click', async () => {
+  stopDepositWatch();
   const urlInput = document.getElementById('url');
   let url = urlInput.value.trim();
   if (!url) return;
@@ -739,6 +793,8 @@ document.getElementById('terms-accept').addEventListener('click', async function
       inv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
       return;
     }
+    // Fixed address: whoever pays can close this invoice and follow the deposit there.
+    if (weLink) weinfoEl.textContent = 'Follow your payment';
     const amountSats = result.min_amount != null ? result.min_amount : minAmount;
     const amountBtc = (amountSats / 1e8).toFixed(8).replace(/\.?0+$/, '');
     const invoiceuri = `bitcoin:${result.address}?amount=${amountBtc}&label=BAL&message=Order+For+url+%26+${encodeURIComponent(url)}`;
@@ -773,6 +829,7 @@ document.getElementById('terms-accept').addEventListener('click', async function
     const inv = document.getElementById('invoice');
     inv.classList.add('show');
     inv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
+    startDepositWatch(result.chain || chain, result.id);
   } catch (err) {
     document.getElementById('iv-status').className = 'err-line';
     document.getElementById('iv-status').textContent = 'Network error. Please try again.';