fix(i18n): move locale files to i18n/locales/ for @nuxtjs/i18n resolution

@nuxtjs/i18n resolves langDir relative to its own i18n/ directory,
not the project root. Moved fr.json and en.json accordingly.

nuxt.config.ts

@@ -35,7 +35,7 @@ export default defineNuxtConfig({
       { code: 'fr', language: 'fr-FR', file: 'fr.json' },
       { code: 'en', language: 'en-US', file: 'en.json' },
     ],
-    langDir: 'app/locales/',
+    langDir: 'locales/',
     detectBrowserLanguage: {
       useCookie: true,
       cookieKey: 'i18n_redirected',