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/hooks/useSocket.ts

@@ -1,13 +1,13 @@
 import { useEffect, useRef, useCallback } from 'react'
 import { io, Socket } from 'socket.io-client'
 import { useGameStore } from '../stores/gameStore'
-import type { GameRoom, ChatMessage, AnswerResult } from '../types'
+import type { GameRoom, ChatMessage, AnswerResult, Achievement } from '../types'
 
 const SOCKET_URL = import.meta.env.VITE_WS_URL || 'http://localhost:8000'
 
 export function useSocket() {
   const socketRef = useRef<Socket | null>(null)
-  const { setRoom, addMessage, setShowStealPrompt, setCurrentQuestion, setTimerEnd } =
+  const { setRoom, addMessage, setShowStealPrompt, setCurrentQuestion, setTimerEnd, setGameResult } =
     useGameStore()
 
   useEffect(() => {
@@ -95,10 +95,34 @@ export function useSocket() {
       console.log(`${data.player_name} reacted with ${data.emoji}`)
     })
 
+    socket.on('game_finished', (data: {
+      room: GameRoom
+      winner: 'A' | 'B' | null
+      final_scores: { A: number; B: number }
+      replay_code: string | null
+      achievements_unlocked: Array<{
+        player_name: string
+        team: 'A' | 'B'
+        achievement: unknown
+      }>
+    }) => {
+      setRoom(data.room)
+      setGameResult({
+        winner: data.winner,
+        finalScores: data.final_scores,
+        replayCode: data.replay_code,
+        achievementsUnlocked: data.achievements_unlocked.map(a => ({
+          player_name: a.player_name,
+          team: a.team,
+          achievement: a.achievement as Achievement
+        }))
+      })
+    })
+
     return () => {
       socket.disconnect()
     }
-  }, [setRoom, addMessage, setShowStealPrompt, setCurrentQuestion, setTimerEnd])
+  }, [setRoom, addMessage, setShowStealPrompt, setCurrentQuestion, setTimerEnd, setGameResult])
 
   // Socket methods
   const createRoom = useCallback((playerName: string) => {