ContourStyle

A contour line's style, expressed as simplestyle-spec property values (stroke, stroke-width, stroke-opacity) rather than a platform color type — both renderers already consume simplestyle properties for imported layers (MapLibre's CustomLayers.kt style expressions; Google's applySimpleStyleSpec()), so a contour feature carrying these properties styles itself identically on both flavors with no per-flavor color logic to keep in sync.

Colors here are a placeholder, not a design-reviewed choice — a topo-map-conventional brown, distinguishable from this app's existing traceroute/geofence palette (both of which already use blue/orange). Needs a pass against the Meshtastic design standards before shipping (constitution principle V), same as any other new on-map visual element.