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>

components/features/features.tsx

@@ -1,4 +1,5 @@
 import { Typography } from "@/components/Typography";
+import { Container } from "@/components/layout/Container";
 
 export type FeaturesProps = {
   tagline: string;
@@ -17,7 +18,7 @@ const colClass: Record<FeaturesProps["columns"], string> = {
 export function Features({ tagline, heading, subheading, columns, items }: FeaturesProps) {
   return (
     <section className="bg-background py-20 md:py-28">
-      <div className="container mx-auto max-w-7xl px-6">
+      <Container>
         <div className="mx-auto mb-16 max-w-2xl text-center">
           {tagline ? (
             <p className="mb-3 text-xs uppercase tracking-[0.2em] text-muted-foreground">
@@ -45,7 +46,7 @@ export function Features({ tagline, heading, subheading, columns, items }: Featu
             </div>
           ))}
         </div>
-      </div>
+      </Container>
     </section>
   );
 }