perf: optimize webapp asset delivery, split admin webapp bundle

frontend/src/adminEntry.js

@@ -0,0 +1,9 @@
+import AdminPanel from "./admin/AdminPanel.svelte";
+import "./styles-admin.css";
+
+window.SubscriptionWebAppAdminPanel = AdminPanel;
+window.dispatchEvent(
+  new CustomEvent("subscription-webapp-admin-ready", {
+    detail: { AdminPanel },
+  })
+);