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>

server/src/engine/customization.ts

@@ -17,7 +17,7 @@ const VALID_ARCHETYPES = new Set([
   'hamster', 'sock_puppet', 'traffic_cone', 'toilet_man', 'potato',
   'cloud_man', 'rock_man', 'balloon_man', 'trash_can', 'rubber_duck',
   'snowman', 'scarecrow', 'jack_o_lantern', 'garden_gnome', 'lamp_post',
-  'broom_man',
+  'broom_man', 'human',
 ])
 
 const HEX_COLOR_RE = /^#[0-9a-fA-F]{6}$/