Sidebar toggle (new HillshadeControl) adds a raster-dem hillshade layer: public Terrarium tiles when online, or a local data/terrain.pmtiles when present (mirrors offline.pmtiles' optional- local-file pattern, new /api/terrain-tiles + /tiles/terrain.pmtiles endpoints). No offline terrain data is bundled, so the toggle is online-only until one is generated — see docs/development.adoc for how.