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/index.html

@@ -186,7 +186,7 @@
             <div class="layer-group-header" data-group="group-infra">
                 <span class="layer-group-chevron">&#9656;</span>
                 <span class="layer-group-title" style="color:#ffdd00">INFRASTRUKTUR</span>
-                <span class="layer-group-count" id="gcount-infra">0/4</span>
+                <span class="layer-group-count" id="gcount-infra">0/5</span>
             </div>
             <div class="layer-group-content">
                 <label class="layer-toggle">
@@ -216,6 +216,7 @@
                     <span class="layer-dot dot-iss"></span>
                     <span class="layer-name">ISS Tracker</span>
                 </label>
+                <label class="layer-toggle">                    <input type="checkbox" id="layer-buildings" title="3D-Gebaeude weltweit aus OpenStreetMap (farbcodiert: Militaer, Industrie, Regierung)">                    <span class="layer-dot dot-buildings"></span>                    <span class="layer-name">3D-Gebaeude</span>                </label>
             </div>
         </div>
 
@@ -337,6 +338,7 @@
     <script src="/static/js/layers/iss.js"></script>
     <script src="/static/js/layers/terminator.js"></script>
     <script src="/static/js/layers/timezones.js"></script>
+    <script src="/static/js/layers/buildings.js"></script>
     <script src="/static/js/layers/firms.js"></script>
     <script src="/static/js/layers/weather.js"></script>
     <script src="/static/js/ui/imagery.js"></script>