Add an option to randomly select 1 Pokemon per location/encounter. This is primarily for open-world games (like Legends: Arceus, Legends: Z-A) where Pokemon are visible in the overworld rather than found through random encounters, but could also be used for other games.
## Checklist
- [ ] Add UI toggle or button to randomize encounters when starting or managing a run
- [ ] Implement random selection logic: pick 1 Pokemon per location from the available encounter list
