Whats the most efficient way to explore all of Zwifts scenic trails without relying on the in-game routing system, and is it possible to create a custom route that combines the best sections of each trail for an ultimate scenic ride challenge, considering factors such as gradient, scenery density, and potential for sprint or KOM opportunities, and what tools or add-ons are available to help riders plan and execute their own custom routes, and do these tools allow for real-time adjustments and navigation during a ride, or are they limited to pre-ride planning and analysis.