🌐 Add full i18n system frontend + API (Story 1.3)

Nuxt i18n with lazy-loaded JSON files, localized routes, hreflang SEO tags,
LanguageSwitcher component. Laravel SetLocale middleware, HasTranslations trait,
API Resources and Controllers for projects/skills with Accept-Language support.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/app/app.vue

@@ -3,3 +3,16 @@
     <NuxtPage />
   </NuxtLayout>
 </template>
+
+<script setup lang="ts">
+const head = useLocaleHead({
+  addDirAttribute: true,
+  addSeoAttributes: true,
+})
+
+useHead({
+  htmlAttrs: computed(() => head.value.htmlAttrs ?? {}),
+  link: computed(() => head.value.link ?? []),
+  meta: computed(() => head.value.meta ?? []),
+})
+</script>