feat: add language selector and lazy-load i18n infrastructure

Updated i18n.ts with SUPPORTED_LOCALES, setLocale() lazy loading,
localStorage persistence. Added language selector in Settings.vue.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/i18n.ts

@@ -3,13 +3,46 @@ import en from './locales/en.json'
 
 export type MessageSchema = typeof en
 
-const i18n = createI18n<[MessageSchema], 'en'>({
+export const SUPPORTED_LOCALES = [
+  { code: 'en', name: 'English', flag: '🇬🇧' },
+  { code: 'es', name: 'Español', flag: '🇪🇸' },
+] as const
+
+export type SupportedLocale = typeof SUPPORTED_LOCALES[number]['code']
+
+const savedLocale = (typeof localStorage !== 'undefined'
+  ? localStorage.getItem('neode_locale')
+  : null) as SupportedLocale | null
+
+const i18n = createI18n({
   legacy: false,
-  locale: 'en',
+  locale: savedLocale || 'en',
   fallbackLocale: 'en',
   messages: {
     en,
   },
 })
 
+/** Lazy-load a locale's messages and switch to it. */
+export async function setLocale(locale: SupportedLocale) {
+  if (locale === 'en') {
+    i18n.global.locale = 'en' as never
+    localStorage.setItem('neode_locale', 'en')
+    return
+  }
+
+  if (!(i18n.global.availableLocales as string[]).includes(locale)) {
+    const messages = await import(`./locales/${locale}.json`)
+    ;(i18n.global as ReturnType<typeof createI18n>['global']).setLocaleMessage(locale, messages.default)
+  }
+
+  i18n.global.locale = locale as never
+  localStorage.setItem('neode_locale', locale)
+}
+
+// Load saved locale on startup
+if (savedLocale && savedLocale !== 'en') {
+  setLocale(savedLocale)
+}
+
 export default i18n