feat: game practice loop with audio, scoring, and level-up modal (Task 11)

- useMorseAudio: wraps MorseAudioEngine, exposes currentSignal for FlashArea
- useProgress: fetches /api/progress + /api/mnemonics, recordAnswer with local stats
- FlashArea: gold flash on signal, height varies dot/dash
- ScoreBar: level name, score, streak display
- PracticeCard: play button, answer input, correct/incorrect feedback with mnemonic
- GamePage: full practice loop, level-up modal at streak%10, anti-repeat history
- Fix: incorrect attempt recorded only once per challenge (no stat inflation on retries)

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

client/src/hooks/useMorseAudio.ts

@@ -0,0 +1,38 @@
+import { useRef, useState, useCallback } from 'react'
+import { MorseAudioEngine } from '../lib/audio'
+import { DEFAULT_WPM } from '../lib/morse'
+
+type SignalType = 'dot' | 'dash' | null
+
+export function useMorseAudio() {
+  const engineRef = useRef<MorseAudioEngine | null>(null)
+  const [isPlaying, setIsPlaying] = useState(false)
+  const [currentSignal, setCurrentSignal] = useState<SignalType>(null)
+
+  function getEngine() {
+    if (!engineRef.current) {
+      const engine = new MorseAudioEngine()
+      engine.on('signal-start', ({ type }: { type: 'dot' | 'dash' }) => setCurrentSignal(type))
+      engine.on('signal-end', () => setCurrentSignal(null))
+      engine.on('play-end', () => { setIsPlaying(false); setCurrentSignal(null) })
+      engineRef.current = engine
+    }
+    return engineRef.current
+  }
+
+  const play = useCallback((text: string) => {
+    const engine = getEngine()
+    engine.stop()
+    setIsPlaying(true)
+    setCurrentSignal(null)
+    engine.play(text, DEFAULT_WPM)
+  }, [])
+
+  const stop = useCallback(() => {
+    engineRef.current?.stop()
+    setIsPlaying(false)
+    setCurrentSignal(null)
+  }, [])
+
+  return { play, stop, isPlaying, currentSignal }
+}