update el runtime to v1.2.0, refactor checkout script to external asset

src/checkout.el

@@ -490,21 +490,7 @@ fn checkout_page(plan: String, pub_key: String) -> String {
 <script>window.NEURON_CFG=window.NEURON_CFG||{};window.NEURON_CFG.plan=\"" + plan + "\";window.NEURON_CFG.pub_key=\"" + pub_key + "\";</script><script src=\"/assets/js/e708dcbb3e7a.js\" defer></script>
 
 " + (if is_free { "
-<script>
-(function(){
-  // Free tier: reveal payment section only after the user has created / signed in.
-  // The existing checkout JS sets auth-badge visible on successful auth — watch for that.
-  var pay = document.getElementById('payment-section');
-  if (!pay) return;
-  var timer = setInterval(function(){
-    var badge = document.getElementById('auth-badge');
-    if (badge && badge.offsetParent !== null) {
-      pay.style.display = '';
-      clearInterval(timer);
-    }
-  }, 150);
-})();
-</script>
+<script src=\"/assets/js/7eac0621cbca.js\" defer></script>
 " } else { "" }) + "
 "
 }