feat(i18n): routing and localization infrastructure (phase 1)

Implement Phase 1 of i18n spec:
- Configure next-intl with 6 locales (pt, en, es, fr, de, zh-CN) and pathnames
- Move routes to app/[locale] structure with localized layouts and metadata
- Add middleware for root language negotiation (307), legacy redirects (308), and 404 for non-pt book
- Implement language selector dropdown in header with cookie persistence
- Add system typography rules for zh-CN and word-break/hyphenation for de/fr

Co-Authored-By: Antigravity <noreply@google.com>

middleware.js

@@ -0,0 +1,102 @@
+import createMiddleware from "next-intl/middleware";
+import { NextResponse } from "next/server";
+import { routing } from "./i18n/routing";
+
+const intlMiddleware = createMiddleware(routing);
+
+const SUPPORTED_LOCALES = routing.locales;
+
+function parseAcceptLanguage(header) {
+	if (!header) return [];
+	return header
+		.split(",")
+		.map((part) => {
+			const [langRange, qPart] = part.trim().split(";");
+			let q = 1.0;
+			if (qPart) {
+				const match = qPart.match(/q=([\d.]+)/);
+				if (match) {
+					const parsed = parseFloat(match[1]);
+					if (!isNaN(parsed)) q = parsed;
+				}
+			}
+			return { lang: langRange.trim().toLowerCase(), q };
+		})
+		.sort((a, b) => b.q - a.q);
+}
+
+function matchLocale(lang) {
+	if (lang.startsWith("pt")) return "pt";
+	if (lang.startsWith("es")) return "es";
+	if (lang.startsWith("fr")) return "fr";
+	if (lang.startsWith("de")) return "de";
+	if (lang.startsWith("zh")) return "zh-CN";
+	if (lang.startsWith("en")) return "en";
+	return null;
+}
+
+function resolveRootLocale(request) {
+	const cookieValue = request.cookies.get("NEXT_LOCALE")?.value;
+	if (cookieValue && SUPPORTED_LOCALES.includes(cookieValue)) {
+		return cookieValue;
+	}
+	const acceptLang = request.headers.get("accept-language");
+	const parsed = parseAcceptLanguage(acceptLang);
+	for (const { lang } of parsed) {
+		const matched = matchLocale(lang);
+		if (matched) return matched;
+	}
+	return "en";
+}
+
+export default function middleware(request) {
+	const { pathname, search } = request.nextUrl;
+
+	// Exclusões de caminhos e arquivos estáticos
+	if (
+		pathname.startsWith("/api") ||
+		pathname.startsWith("/_next") ||
+		pathname === "/robots.txt" ||
+		pathname === "/sitemap.xml" ||
+		pathname === "/google21a790a2c23c0ec5.html" ||
+		/\.[a-zA-Z0-9]+$/.test(pathname)
+	) {
+		return NextResponse.next();
+	}
+
+	// 1. Raiz: negociação de idioma (307)
+	if (pathname === "/") {
+		const targetLocale = resolveRootLocale(request);
+		const url = new URL(`/${targetLocale}/`, request.url);
+		url.search = search;
+		const response = NextResponse.redirect(url, 307);
+		response.headers.set("Vary", "Accept-Language, Cookie");
+		response.headers.set("Cache-Control", "private, no-store");
+		return response;
+	}
+
+	// 2. Livro fora do português: 404
+	if (/^\/(en|es|fr|de|zh-CN)\/livro(\/.*)?$/.test(pathname)) {
+		return new NextResponse(null, { status: 404 });
+	}
+
+	// 3. URLs antigas sem prefixo reconhecido: redirecionamento 308 para /pt/<caminho>
+	const hasLocalePrefix = SUPPORTED_LOCALES.some(
+		(loc) => pathname === `/${loc}` || pathname.startsWith(`/${loc}/`)
+	);
+
+	if (!hasLocalePrefix) {
+		const url = new URL(`/pt${pathname}`, request.url);
+		url.search = search;
+		return NextResponse.redirect(url, 308);
+	}
+
+	// 4. Delegação para o roteamento do next-intl
+	return intlMiddleware(request);
+}
+
+export const config = {
+	matcher: [
+		"/((?!api|_next|_vercel|.*\\..*|robots\\.txt|sitemap\\.xml|google21a790a2c23c0ec5\\.html).*)",
+	],
+};