feat: 3D-Gebaeude Layer (OSM Buildings via Cesium Ion)

- Weltweite 3D-Gebaeude mit Hoehen aus OpenStreetMap
- Farbcodiert: Militaer (rot), Industrie (orange), Regierung (blau), Rest (grau)
- Toggle in Gruppe INFRASTRUKTUR
- Kostenlos via Cesium Ion OSM Buildings Tileset

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/js/app.js

@@ -185,6 +185,7 @@ const Globe = {
             'layer-nightlights': function(on) { on ? NightlightsLayer.start(Globe.viewer) : NightlightsLayer.stop(); },
             'layer-celltowers': function(on) { on ? CelltowersLayer.start(Globe.viewer) : CelltowersLayer.stop(); },
             'layer-iss': function(on) { on ? ISSLayer.start(Globe.viewer) : ISSLayer.stop(); },
+            'layer-buildings': function(on) { on ? BuildingsLayer.start(Globe.viewer) : BuildingsLayer.stop(); },
             'layer-disasters': function(on) { on ? DisastersLayer.start(Globe.viewer) : DisastersLayer.stop(); },
             'layer-weather': function(on) { on ? WeatherLayer.start(Globe.viewer) : WeatherLayer.stop(); },
             'layer-firms': function(on) { on ? FirmsLayer.start(Globe.viewer) : FirmsLayer.stop(); },