Reactive Shopping Cart with Signals (@preact/signals-core via CDN, No Build Step)

A live shopping cart total that updates with no virtual DOM diffing at all, using @preact/signals-core loaded straight from a CDN as an ES module. Each quantity is a signal(), the subtotal/tax/total are computed() from them, and effect() writes only the exact DOM nodes that depend on a given signal - the fine-grained reactivity model now shared by Preact, Solid, Vue and Angular, without adopting any of those frameworks.