Element: #162 Horizontal stepper (navigation/stepper)
What it shows: A four-step horizontal stepper inside a glass card with Back and Next buttons that advance the step.
When to use: Multi-step flows such as onboarding or checkout where the user moves through ordered stages.
Spec:
- `` with `let step = $state(0)`
- `const steps` has 4 entries with a `label` field: Account, Profile, Billing, Review
- Wrapper is `` with ``
- Body shows `Step {step + 1}: {steps[step].label}`
- Back is `