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/layers/buildings.js

@@ -0,0 +1,36 @@
+/**
+ * 3D-Gebaeude-Layer: OpenStreetMap Buildings via Cesium Ion.
+ * Zeigt weltweite 3D-Gebaeude mit Hoehen aus OSM-Daten.
+ */
+const BuildingsLayer = {
+    _viewer: null,
+    _tileset: null,
+
+    start: function(viewer) {
+        if (this._tileset) return;
+        this._viewer = viewer;
+        var self = this;
+        Cesium.createOsmBuildingsAsync().then(function(tileset) {
+            if (!self._viewer) return;
+            self._tileset = tileset;
+            self._tileset.style = new Cesium.Cesium3DTileStyle({
+                color: {
+                    conditions: [
+                        ["${feature['building']} === 'military'", "color('#ff2222', 0.7)"],
+                        ["${feature['building']} === 'industrial'", "color('#ff8800', 0.6)"],
+                        ["${feature['building']} === 'government' || ${feature['building']} === 'public'", "color('#4488ff', 0.6)"],
+                        ["true", "color('#88aacc', 0.45)"],
+                    ],
+                },
+            });
+            self._viewer.scene.primitives.add(self._tileset);
+        });
+    },
+
+    stop: function() {
+        if (this._tileset && this._viewer) {
+            this._viewer.scene.primitives.remove(this._tileset);
+            this._tileset = null;
+        }
+    },
+};