Pricing — 4 tiers with enterprise

Create pricing — 4 tiers with enterprise.

Spec: Four tiers including enterprise with 'Talk to us' instead of price.

Build with:
- Tailwind 4 + shadcn/ui primitives
- Fully responsive (stacks on mobile)
- Dark mode via next-themes
- Accessible: labels, aria where needed, keyboard nav
- TypeScript props

Return a single self-contained React component. Include mock data inline so it renders standalone.