Add runnable example for workout protocol execution

[josedab]

What

The examples/ directory has quickstart.ts, analyze.ts, and training.ts but no example showing the WorkoutEngine executing a protocol with real-time step tracking.

Where

• New example: examples/workout.ts
• Add script to: examples/package.json

How

1. Use MockTransport for a Tabata protocol
2. Show WorkoutEngine step progression and target compliance events
3. Make it runnable via pnpm --filter @hrkit/examples workout

Acceptance Criteria

• Example runs without errors
• Script added to package.json
• Demonstrates step changes and target compliance