🌐 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/en.json

@@ -0,0 +1,37 @@
+{
+  "nav": {
+    "home": "Home",
+    "projects": "Projects",
+    "skills": "Skills",
+    "testimonials": "Testimonials",
+    "journey": "Journey",
+    "contact": "Contact",
+    "resume": "Quick Resume"
+  },
+  "common": {
+    "continue": "Continue",
+    "back": "Back",
+    "discover": "Discover",
+    "close": "Close",
+    "loading": "Loading...",
+    "language": "Language"
+  },
+  "landing": {
+    "title": "Welcome to my universe",
+    "subtitle": "Full-Stack Developer",
+    "cta_adventure": "Start the adventure",
+    "cta_express": "Express mode"
+  },
+  "error": {
+    "404": "Page not found",
+    "generic": "An error occurred"
+  },
+  "meta": {
+    "title": "Skycel - Célian's Portfolio",
+    "description": "Discover my interactive and gamified portfolio"
+  },
+  "footer": {
+    "copyright": "© {year} Célian — Skycel",
+    "built_with": "Built with Nuxt & Laravel"
+  }
+}