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/css/globe.css

@@ -795,6 +795,7 @@ html, body { height: 100%; overflow: hidden; background: var(--bg-primary); colo
 .dot-nightlights { background: #ffd740; box-shadow: 0 0 4px rgba(255,215,64,0.4); }
 .dot-celltowers { background: #e040fb; }
 .dot-firms { background: #ff4400; box-shadow: 0 0 4px rgba(255,68,0,0.4); }
+.dot-buildings { background: #88aacc; box-shadow: 0 0 4px rgba(136,170,204,0.4); }
 
 .geoint-btn-row {
     display: flex;