Add language switcher dropdown and persist manual locale choice.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/i18n.ts

@@ -12,6 +12,7 @@ export type Dictionary = {
   heroTagline: string;
   heroTaglineLine2: string;
   copyright: string;
+  languageLabel: string;
   liveBadge: string;
   entryCards: Record<string, EntryCardCopy>;
   about: {
@@ -35,6 +36,7 @@ export const dictionaries: Record<Locale, Dictionary> = {
     heroTagline: "游民导航 · 地理套利 · 直播工具箱",
     heroTaglineLine2: "一站开启自由生活",
     copyright: "© {year} Nomadro",
+    languageLabel: "语言",
     liveBadge: "LIVE",
     entryCards: {
       nav: {
@@ -72,6 +74,7 @@ export const dictionaries: Record<Locale, Dictionary> = {
     heroTagline: "Nomad Nav · Geo Arbitrage · Live Toolkit",
     heroTaglineLine2: "Your freedom lifestyle, in one place",
     copyright: "© {year} Nomadro",
+    languageLabel: "Language",
     liveBadge: "LIVE",
     entryCards: {
       nav: {