feat: omni-morph sprite swap, bullet time showboats, music tuning, server hardening

- Creator omni-morph now generates actual sprite sheets for morphed archetypes
- 3 new Creator showboats: bullet time attack, ₿ throne summon, disco dance
- Music: subtle tempo shift (+10 BPM max), longer phrases (8/16/24 bars),
  smoother crossfades, less chaotic hi-hat at high intensity
- Server: security headers, body size limit, production error masking,
  CORS origin warning, graceful shutdown with drain
- Payments: atomic consume (eliminates SELECT/UPDATE race), release reverts DB
- Fight loop: round events for live TUI, retro displayPrompt
- Frontend: pass pubkey in payment/queue requests

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

server/src/engine/retro-moves.ts

@@ -122,12 +122,14 @@ export function generateRetroChallenge(): Challenge {
 
   const moveList = knownMoves.map(m => `  ${m.input} = ${m.name} (${m.damage} dmg)`).join('\n')
 
+  const displayPrompt = 'Binary Gamepads at the ready, GO!'
   const prompt = `ARCADE ROUND! Pick 3 moves:\n${moveList}\n\nSecret combos exist — longer chains hit harder.\nAnswer: combo1 | combo2 | combo3`
 
   return {
     type: 'retro_mode',
     label: 'Retro Mode',
     prompt,
+    displayPrompt,
     answers: knownInputs,
     timeout_ms: 12000,
     scoring: 'factual',