Add an elevation widget

> Hi all, I would LOVE to see current elevation AND trend (say, about current trip, or last X km/miles) with an upward/downward arrow overlayed onto the map...feasible?

https://discord.com/channels/1313185644134006886/1325846450206277632

would be neat to have a widget showing the elevation of the route and your progress along it

Start by reviewing the map and route-rendering entry points, then read the linked Discord discussion for context. Define the widget's elevation source, trend window, units, and route-progress behavior before implementation; done means the map displays current elevation, trend direction, and progress consistently.

Written by the indexing model from the issue text.