feat(docs): enhance documentation site with internationalization and layout updates

- Updated the demo API to support locale-based content rendering.
- Refactored the main layout to accommodate language-specific metadata and routing.
- Introduced new components for blog and documentation pages, ensuring proper language handling.
- Added styles for improved UI consistency across different sections.
- Removed deprecated layout files and streamlined the structure for better maintainability.

apps/docs/proxy.ts

@@ -1,5 +1,7 @@
-import { NextRequest, NextResponse } from 'next/server';
+import { NextRequest, NextResponse, type NextFetchEvent } from 'next/server';
 import { isMarkdownPreferred, rewritePath } from 'fumadocs-core/negotiation';
+import { createI18nMiddleware } from 'fumadocs-core/i18n/middleware';
+import { i18n, type Language } from '@/lib/i18n';
 import { docsContentRoute, docsRoute } from '@/lib/shared';
 
 const { rewrite: rewriteDocs } = rewritePath(
@@ -11,22 +13,41 @@ const { rewrite: rewriteSuffix } = rewritePath(
   `${docsContentRoute}{/*path}/content.md`,
 );
 
-export default function proxy(request: NextRequest) {
-  const result = rewriteSuffix(request.nextUrl.pathname);
-  if (result) {
-    return NextResponse.rewrite(new URL(result, request.nextUrl));
+const i18nMiddleware = createI18nMiddleware(i18n);
+
+/** Split the locale prefix (if any) from a pathname. */
+function splitLocale(pathname: string): { locale: Language; rest: string } {
+  for (const lang of i18n.languages) {
+    if (pathname === `/${lang}`) return { locale: lang, rest: '/' };
+    if (pathname.startsWith(`/${lang}/`)) {
+      return { locale: lang, rest: pathname.slice(lang.length + 1) };
+    }
+  }
+  return { locale: i18n.defaultLanguage, rest: pathname };
+}
+
+export default function proxy(request: NextRequest, event: NextFetchEvent) {
+  const { locale, rest } = splitLocale(request.nextUrl.pathname);
+
+  const suffixTarget = rewriteSuffix(rest);
+  if (suffixTarget) {
+    return NextResponse.rewrite(new URL(`/${locale}${suffixTarget}`, request.nextUrl));
   }
 
   if (isMarkdownPreferred(request)) {
-    const result = rewriteDocs(request.nextUrl.pathname);
+    const target = rewriteDocs(rest);
 
-    if (result) {
-      return NextResponse.rewrite(new URL(result, request.nextUrl), {
+    if (target) {
+      return NextResponse.rewrite(new URL(`/${locale}${target}`, request.nextUrl), {
         // this URL has two representations, selected by `Accept`
         headers: { Vary: 'Accept' },
       });
     }
   }
 
-  return NextResponse.next();
+  return i18nMiddleware(request, event);
 }
+
+export const config = {
+  matcher: ['/((?!api|_next|favicon.ico|images/|product-demo/|llms\\.txt|llms-full\\.txt).*)'],
+};