Create a Button component for the Outer Edge Design System.

Stack: Next.js App Router, shadcn/ui, Tailwind CSS, Inter font.
Path: @/components/ui/button
Build with: class-variance-authority (cva), cn() from @/lib/utils

Variants:
- default: bg-neutral-900 text-white hover:bg-neutral-800
- outline: border border-neutral-300 text-neutral-900 hover:bg-neutral-50
- secondary: bg-neutral-100 text-neutral-900 hover:bg-neutral-200
- ghost: transparent text-neutral-900 hover:bg-neutral-100
- link: text-neutral-900 underline-offset-4 hover:underline

Sizes:
- default: h-10 px-4 py-2 text-sm
- sm: h-9 px-3 text-xs
- lg: h-11 px-8 text-base
- icon: h-10 w-10

Styling rules:
- Font: Inter, font-medium
- Border radius: rounded (0.25rem via --radius CSS variable)
- Transition: transition-colors
- Disabled state: opacity-50 cursor-not-allowed pointer-events-none
- Focus: focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-neutral-950 focus-visible:ring-offset-2

Color palette (neutral only):
- neutral-900: #171717 | neutral-800: #262626
- neutral-100: #f5f5f5 | neutral-50: #fafafa
- neutral-300: #d4d4d4 (borders)

Accessibility:
- Render as <button> by default, support asChild for polymorphic usage
- Always use verb labels: "Save changes" not "Submit"
- Disabled buttons must not be focusable

Export both Button component and buttonVariants.