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>

app/globals.css

@@ -759,4 +759,28 @@
 	.no-scrollbar::-webkit-scrollbar {
 		display: none;
 	}
+
+	/* ------------------------------------------------------------------------
+	   Tipografia e layout internacionalizados (seção 9b da spec)
+	   ------------------------------------------------------------------------ */
+	html[lang="zh-CN"] {
+		font-family: "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", "Noto Sans SC", sans-serif;
+		letter-spacing: 0;
+		line-height: 1.7;
+	}
+
+	html[lang="zh-CN"] code,
+	html[lang="zh-CN"] pre,
+	html[lang="zh-CN"] kbd {
+		font-family: var(--font-mono);
+	}
+
+	html[lang="de"],
+	html[lang="fr"] {
+		hyphens: auto;
+	}
+
+	p, li, dd {
+		overflow-wrap: anywhere;
+	}
 }