feat: human vs AI mode — live typing challenges, baby growth system, SSE rounds

- Add choose-mode step: "I BUILD BOTS" vs "I FIGHT MYSELF" paths
- Human registration with baby avatar picker, no webhook required
- Live fight scene with SSE round streaming and real-time challenge UI
- 5-second timer per round, submit answers via browser
- Baby → toddler → kid → teen → adult → hero → super growth stages
- Huge sparkly baby eyes, diapers, pacifiers, bibs, rattles, rosy cheeks
- Speech bubble positioning fix (pushed to outside of sprite)
- Canvas text rendering via offscreen canvas to bypass kaplay color issues
- Voice timing improvements: await pauses between voice lines and hits
- 30 devastating announcement lines, 15 critical/hit word variants
- Orchestrator human player detection + waitForHumanResponse system
- Server endpoints: GET /challenge/:botId, POST /respond/:botId
- Human player auth: register-human route, isHuman flag on login

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

frontend/src/game/sounds.ts

@@ -269,7 +269,9 @@ function speak(text: string, profileName: string, cancelPrevious: boolean = fals
   if (typeof speechSynthesis === 'undefined') return
   if (masterMuted) return
   if (!voicesLoaded) loadVoices()
-  if (cancelPrevious) speechSynthesis.cancel()
+  // Always cancel queued speech — only the most recent line matters
+  // This prevents stale voiceovers from playing seconds after their visual moment
+  speechSynthesis.cancel()
   const profile = voiceProfiles[profileName] || voiceProfiles.announcer
   const utter = new SpeechSynthesisUtterance(text)
   if (profile.voice) utter.voice = profile.voice
@@ -290,6 +292,7 @@ export function announce(text: string, pitch?: number, rate?: number) {
   if (pitch !== undefined || rate !== undefined) {
     if (typeof speechSynthesis === 'undefined') return
     if (!voicesLoaded) loadVoices()
+    speechSynthesis.cancel() // cancel previous to stay in sync with visuals
     const utter = new SpeechSynthesisUtterance(text)
     const profile = voiceProfiles.announcer
     if (profile.voice) utter.voice = profile.voice