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.

weinfo.html

@@ -36,6 +36,7 @@
       <h2 id="wename">&nbsp;</h2>
       <h3 id="weinfo">&nbsp;</h3>
       <h4 id="wechain">&nbsp;</h4>
+      <div id="wepayment" style="display:none;max-width:640px;margin:10px auto 18px;padding:10px 14px;border-radius:8px;font-weight:600"></div>
     </div>
     <div style="float:left;border:1;margin-right:50px;">
       <div><span>Version:</span><span id="weversion">&nbsp;</span></div>
@@ -77,6 +78,69 @@
     </div>
     <a href="" id="download">Download</a>
     <script type="text/javascript"> 
+      // Payment banner: this page has a fixed address, so whoever paid can close the
+      // invoice and follow the deposit here. It asks the server data every 30 seconds
+      // until the server is listed. The status only moves forward, because
+      // unconfirmed_balance may go back to 0 before the deposit is credited.
+      const PAYMENT_POLL_MS = 30000;
+      const PAYMENT_POLL_MAX_MS = 24 * 60 * 60 * 1000;
+      const paymentStarted = Date.now();
+      let paymentTimer = null, paymentSeen = false, paymentAmount = 0, firstExpiry;
+
+      function showPayment(text, ok) {
+        const box = document.getElementById('wepayment');
+        box.textContent = text;
+        box.style.display = 'block';
+        box.style.color = ok ? '#14703a' : '#7a5200';
+        box.style.background = ok ? '#e6f6ec' : '#fdf3dc';
+      }
+
+      function stopPayment() {
+        if (paymentTimer) clearInterval(paymentTimer);
+        paymentTimer = null;
+      }
+
+      async function pollPayment() {
+        if (Date.now() - paymentStarted > PAYMENT_POLL_MAX_MS) return stopPayment();
+        const path = window.location.pathname.split('/').filter(p => p !== '');
+        let data;
+        try {
+          const response = await fetch('/weinfodata/' + path[1] + '/' + path[2]);
+          if (!response.ok) return;
+          data = await response.json();
+        } catch (err) {
+          return;  // temporary network problem: try again at the next round
+        }
+        if (!data) return;
+        const expiry = data.expiry_date || null;
+        if (firstExpiry === undefined) firstExpiry = expiry;
+        const unconfirmed = Number(data.unconfirmed_balance) > 0;
+        const active = expiry && new Date(expiry.replace(' ', 'T') + 'Z') > new Date();
+        const bal = data.balance != null ? data.balance : null;
+        const unc = data.unconfirmed_balance != null ? data.unconfirmed_balance : null;
+        document.getElementById('webalance').textContent = bal ? (unc ? bal + ' (' + unc + ')' : bal) : '—';
+        const expiryCell = document.createElement('b');
+        expiryCell.textContent = expiry || '—';
+        document.getElementById('weexpiry').replaceChildren(expiryCell);
+        if (expiry && expiry !== firstExpiry) {
+          showPayment('✓ Payment confirmed: this server is now listed.', true);
+          stopPayment();
+        } else if (unconfirmed || paymentSeen) {
+          paymentSeen = true;
+          if (unconfirmed) paymentAmount = Number(data.unconfirmed_balance);
+          showPayment('Payment detected: ' + paymentAmount.toLocaleString('en-US') + ' sats, waiting for 3 confirmations (about 30 minutes). This page updates by itself.', false);
+        } else if (active) {
+          stopPayment();  // already listed and nothing incoming: no banner, nothing to follow
+        } else {
+          showPayment('Waiting for payment. This page updates by itself.', false);
+        }
+      }
+
+      document.addEventListener('DOMContentLoaded', () => {
+        paymentTimer = setInterval(pollPayment, PAYMENT_POLL_MS);
+        pollPayment();
+      });
+
       function getWeInfo(){
         const path = window.location.pathname.split('/').filter(p => p !== '');
         const we_id = path[2];