Add Container component and fix radius/maxWidth theming

- Drop buttonRadius prop; button now uses --radius via rounded-md
- Inject @theme radius mappings into ThemeProvider so rounded-* utilities
  pick up --radius inside the Tailwind CDN iframe
- Add shared Container that consumes --container-max-width set from the
  global maxWidth prop, replacing ad-hoc "container mx-auto max-w-7xl px-6"
  wrappers across commerce, landing, footer, navigation, and others
- Simplify maxWidth options to Small/Medium/Large/X-Large/Full bleed and
  shift the scale up so Large (1280px) matches the previous default

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/globals.css

@@ -32,7 +32,6 @@
   --radius-md: calc(var(--radius) * 0.75);
   --radius-lg: var(--radius);
   --radius-xl: calc(var(--radius) * 1.5);
-  --radius-button: var(--button-radius, var(--radius));
 
   --animate-marquee: marquee var(--duration) infinite linear;
   --animate-marquee-vertical: marquee-vertical var(--duration) linear infinite;