Add interactive 3D model viewer

Replace static 3D image with a draggable, interactive GLB model viewer in the Hero section. Introduce Building3DViewer component, load model from public/models/building-model.glb, and integrate with Hero.tsx replacing previous placeholder. Includes OrbitControls, lighting, and responsive sizing. X-Lovable-Edit-ID: edt-cca9d247-ac4f-4120-b4ac-987b75c404df