Workout export

Hi,
Great skill! However, the exported workout lacks structure; e.g., for 4x2 min run interval training, only one long interval is exported. The exported .zwo shown below is from the Examples [5K Training Plan](https://felixrieseberg.github.io/claude-coach/demos/5k-beginner.html), but it's the same for my custom-generated plan.

**.zwo file**
```

Claude Coach
Walk/Run Intervals
Aerobic development

WARM-UP: 5 min easy walk

MAIN SET:
4x (2 min run / 2 min walk)
Focus on relaxed form
Shoulders down, arms relaxed

COOL-DOWN: 4 min easy walk
run

```