fix(toast): rename Nuxt UI 4 toast.add timeout → duration

Nuxt UI 4's Toast component reads `duration` (default 5000ms), not
`timeout` — the property was silently ignored. Behavior unchanged
since 5000ms matched the default. Fix the call site to be honest.

Strike the now-resolved gotcha from LAUNCH_READINESS.md.

app/components/SeriesPassPurchase.vue

@@ -308,7 +308,7 @@ const handleSubmit = async () => {
       title: "Series Pass Purchased!",
       description: `You're now registered for all ${purchaseResponse.registration.eventsRegistered} events in this series.`,
       color: "green",
-      timeout: 5000,
+      duration: 5000,
     });
 
     // Emit success event
@@ -328,7 +328,7 @@ const handleSubmit = async () => {
       title: "Purchase Failed",
       description: errorMessage,
       color: "red",
-      timeout: 5000,
+      duration: 5000,
     });
 
     emit("purchase-error", errorMessage);