🌐 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/i18n/fr.json

@@ -0,0 +1,37 @@
+{
+  "nav": {
+    "home": "Accueil",
+    "projects": "Projets",
+    "skills": "Compétences",
+    "testimonials": "Témoignages",
+    "journey": "Parcours",
+    "contact": "Contact",
+    "resume": "Résumé Express"
+  },
+  "common": {
+    "continue": "Continuer",
+    "back": "Retour",
+    "discover": "Découvrir",
+    "close": "Fermer",
+    "loading": "Chargement...",
+    "language": "Langue"
+  },
+  "landing": {
+    "title": "Bienvenue dans mon univers",
+    "subtitle": "Développeur Full-Stack",
+    "cta_adventure": "Partir à l'aventure",
+    "cta_express": "Mode express"
+  },
+  "error": {
+    "404": "Page non trouvée",
+    "generic": "Une erreur est survenue"
+  },
+  "meta": {
+    "title": "Skycel - Portfolio de Célian",
+    "description": "Découvrez mon portfolio interactif et gamifié"
+  },
+  "footer": {
+    "copyright": "© {year} Célian — Skycel",
+    "built_with": "Construit avec Nuxt & Laravel"
+  }
+}