Reaction Game (Juego de Reflejos)

Implement the core timing logic for a reaction-speed game.

Write two functions:

1. startGame() — returns initial game state { phase: 'wait', score: 0, delay: number } with random 1-5s delay
2. handleTap(state, now) — processes a tap at timestamp now, returns updated state

Rules:

• Phase 'wait': ignore taps
• Phase 'active': record reaction time (now - targetShown), increment score, transition to 'wait' with new random delay
• Game ends after 10 seconds total (handle in UI)
• Phase 'result': game over, show final score