fix(web): drop nested <main> on manifesto (WCAG 1.3.1)

LocalizedPageShell at app/_components/localized-page-shell.tsx:34
already renders <main className='flex-1'>{children}</main> as the
page landmark. The manifesto/page.tsx shell was wrapping that with
its own <main>, producing nested main landmarks (axe-core:
landmark-no-duplicate-main + landmark-main-is-top-level).

Switch outer wrapper to <div>; keep styling (bg-background,
text-foreground, min-h-screen, overflow-x-hidden) intact. The
inner <main> from the shell remains the canonical landmark.

Pre-existing on origin/dev (the pre-decomposition manifesto/page.tsx
also had a top-level <main>), surfaced by PR #4202 hands-on QA
via axe-core run on /ko/manifesto.

packages/web/app/[locale]/manifesto/page.tsx

@@ -12,7 +12,7 @@ import { Separator } from "@/components/ui/separator"
 
 export default async function ManifestoPage(): Promise<JSX.Element> {
   return (
-    <main className="bg-background text-foreground min-h-screen overflow-x-hidden">
+    <div className="bg-background text-foreground min-h-screen overflow-x-hidden">
       <HeroSection />
       <PainPointsSection />
       <Separator className="mx-auto max-w-4xl opacity-20" />
@@ -24,6 +24,6 @@ export default async function ManifestoPage(): Promise<JSX.Element> {
       <CoreLoopSection />
       <FutureSection />
       <FinalCtaSection />
-    </main>
+    </div>
   )
 }