Add theme toggle, hero snippet, and reorganize homepage components

- Set up next-themes with a light/dark toggle in the header and move all
  sections onto theme tokens; dark mode stays pure black
- Replace the hero terminal line with the AI Elements Snippet component
- Restructure components into layout/, sections/, and shared/ with
  site-wide config in lib/site.ts

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

components/sections/cta-section.tsx

@@ -0,0 +1,25 @@
+import { ActionButtons } from '@/components/shared/action-buttons';
+import { Container } from '@/components/shared/container';
+import { GradientGlow } from '@/components/shared/gradient-glow';
+import { SectionHeading } from '@/components/shared/section-heading';
+
+export function CtaSection() {
+  return (
+    <section className="relative overflow-hidden">
+      <GradientGlow className="left-1/2 top-1/2 h-[300px] w-[600px] -translate-x-1/2 -translate-y-1/2 opacity-25" />
+      <Container className="relative py-28">
+        <SectionHeading
+          align="center"
+          title="Ship your first project in minutes."
+          description="Import a repository or start from a template. No credit card required to deploy your first preview."
+          className="[&>h2]:text-4xl sm:[&>h2]:text-5xl"
+        />
+        <ActionButtons
+          className="mt-9"
+          primary={{ label: 'Start Deploying', href: '#' }}
+          secondary={{ label: 'Talk to Sales', href: '#' }}
+        />
+      </Container>
+    </section>
+  );
+}