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/landing/newsletter-cta.tsx

@@ -1,6 +1,7 @@
 import { useState } from "react";
 import { cn } from "@/lib/utils";
 import { Typography } from "@/components/Typography";
+import { Container } from "@/components/layout/Container";
 
 export type EmailProvider = "none" | "mailchimp" | "klaviyo";
 
@@ -131,7 +132,7 @@ export function NewsletterCta({
   if (layout === "split") {
     return (
       <section className="bg-background">
-        <div className="container mx-auto max-w-7xl px-6 py-16 md:py-24">
+        <Container className="py-16 md:py-24">
           <div className="grid grid-cols-1 items-center gap-12 md:grid-cols-2">
             <div>
               {imageUrl ? (
@@ -165,7 +166,7 @@ export function NewsletterCta({
               </div>
             </div>
           </div>
-        </div>
+        </Container>
       </section>
     );
   }