feat(phase4): Complete frontend with themes, replay, and results

Visual Effects:
- Add effects.css with neon glow, CRT scanlines, glitch, sparkles, RGB shift
- Animations work with all 5 themes (DRRR, Retro, Minimal, RGB, Anime)

Game Finished Handler:
- Add gameResult state to gameStore (winner, scores, replay, achievements)
- Handle game_finished WebSocket event in useSocket
- Store achievements unlocked by all players

Results Page:
- Show winner with animation (or tie)
- Display final scores with staggered animation
- List achievements unlocked per player
- Buttons for replay and new game

Replay Player:
- Fetch replay from API by code
- Auto-playback with configurable speed (1x, 2x, 4x)
- Play/Pause and timeline controls
- Events sidebar for navigation
- Animated event transitions

Lobby Updates:
- Load categories from API on mount
- Display available categories with icons
- Backend generates board (no hardcoded data)

TypeScript Fixes:
- Add vite-env.d.ts for import.meta.env types
- Fix ringColor style issues
- Remove unused imports

Build verified: npm run build succeeds

Phase 4 tasks completed:
- F4.1: CSS effects for themes
- F4.2: Results page with achievements
- F4.3: Replay player
- F4.4: game_finished handler
- F4.5: Lobby API integration
- F4.6: Build verification and fixes

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

frontend/src/pages/Game.tsx

@@ -19,7 +19,7 @@ const categories = [
 ]
 
 export default function Game() {
-  const { roomCode } = useParams<{ roomCode: string }>()
+  useParams<{ roomCode: string }>()
   const navigate = useNavigate()
   const { selectQuestion, submitAnswer, stealDecision, sendEmojiReaction } = useSocket()
   const { play } = useSound()
@@ -80,7 +80,7 @@ export default function Game() {
 
   const handleSubmitAnswer = () => {
     if (!currentQuestion || !answer.trim()) return
-    submitAnswer(answer, currentQuestion as Record<string, unknown>, room.can_steal)
+    submitAnswer(answer, currentQuestion as unknown as Record<string, unknown>, room.can_steal)
     setAnswer('')
     setShowingQuestion(false)
   }