fix: pass locale explicitly to Hero and force-dynamic on locale-sensitive API routes

- Hero.tsx: pass locale prop directly to getTranslations instead of
  relying on setRequestLocale async storage, which can be lost during
  Next.js RSC streaming
- book-reviews route: replace revalidate=300 with force-dynamic to
  prevent cached English responses being served to German locale requests
- content/page route: add runtime=nodejs and force-dynamic (was missing
  both, violating CLAUDE.md API route conventions)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/components/Hero.tsx

@@ -5,8 +5,8 @@ interface HeroProps {
   locale: string;
 }
 
-export default async function Hero({ locale: _locale }: HeroProps) {
-  const t = await getTranslations("home.hero");
+export default async function Hero({ locale }: HeroProps) {
+  const t = await getTranslations({ locale, namespace: "home.hero" });
 
   return (
     <section className="relative min-h-screen flex flex-col items-center justify-center bg-stone-50 dark:bg-stone-950 px-6 transition-colors duration-500">