Ka-ching sale notifications

When a paid, non-free order arrives, every open admin tab plays a ka-ching and shows a toast with the amount and event title.

Toggle: Settings → General → “Play sound on sale”. Default on. Off mutes the sound but keeps the toast.

First-sale silence: browsers block audio until you’ve clicked at least once on the page. Click anywhere in the admin once after opening it and every following sale plays cleanly.

What never triggers it: free orders, refunds, cancellations, re-saves of an already-paid order.