🎮 Add landing page with hero selection (Story 1.5)

Landing page with animated tagline, dual CTA (adventure/express), and
HeroSelector component (3 heroes: Recruiter, Client, Developer) with full
keyboard accessibility (radiogroup, arrow nav, Enter confirm). Staggered
CSS animations respecting prefers-reduced-motion. Bilingual FR/EN.

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

frontend/i18n/en.json

@@ -20,9 +20,25 @@
   },
   "landing": {
     "title": "Welcome to my universe",
-    "subtitle": "Full-Stack Developer",
+    "subtitle": "Passionate Full-Stack Developer",
     "cta_adventure": "Start the adventure",
-    "cta_express": "Express mode"
+    "cta_express": "Express mode (30s)"
+  },
+  "hero": {
+    "question": "Who are you, traveler?",
+    "select_label": "Select your profile",
+    "recruteur": {
+      "name": "Recruiter",
+      "description": "I'm looking for a talent to join my team"
+    },
+    "client": {
+      "name": "Client",
+      "description": "I have a project and I'm looking for the right developer"
+    },
+    "dev": {
+      "name": "Developer",
+      "description": "I'm curious to discover your work and skills"
+    }
   },
   "error": {
     "404": "Oops! This page seems to have gotten lost in the code...",