feat: arena bot sprites, boxing-style Fight Card page

- Arena page shows small sprite previews next to each bot's name
- Server returns archetype in fights list endpoint
- New /fight-card page with 3D perspective fight poster, neon signs,
  animated boxing gloves, fighter bobbing, VS pulse, undercard list
- Added FIGHT CARD to nav bar

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/NavBar.vue

@@ -9,6 +9,7 @@ const isMenuOpen = ref(false)
 
 const links = [
   { to: '/join', label: 'FIGHT!' },
+  { to: '/fight-card', label: 'FIGHT CARD' },
   { to: '/arena', label: 'WATCH' },
   { to: '/leaderboard', label: 'RANKINGS' },
   { to: '/docs', label: 'DOCS' },