feat: improve offline PWA resilience

webapp/src/lib/pwa.ts

@@ -3,9 +3,16 @@ export function registerNodeWardenServiceWorker(): void {
   if (!('serviceWorker' in navigator)) return;
   if (import.meta.env.DEV) return;
 
-  window.addEventListener('load', () => {
+  const register = () => {
     void navigator.serviceWorker.register('/sw.js', { scope: '/' }).catch(() => {
       // PWA support is progressive enhancement; the vault still works without it.
     });
-  });
+  };
+
+  if (document.readyState === 'complete') {
+    register();
+    return;
+  }
+
+  window.addEventListener('load', register, { once: true });
 }