Add furniture placement to 3D renderer

- loadCatalog() and loadDesign() methods on HouseRenderer
- Builds Three.js meshes from catalog part definitions (box/cylinder)
- Places furniture in room-local coordinates with rotation
- Furniture clears and re-renders on floor switch
- index.html loads catalog and design after house data

src/index.html

@@ -94,8 +94,10 @@
 
     let selectedRoom = null;
 
-    renderer.loadHouse('../data/sample-house.json').then(house => {
+    renderer.loadHouse('../data/sample-house.json').then(async (house) => {
       document.getElementById('house-name').textContent = house.name;
+      await renderer.loadCatalog('../data/furniture-catalog.json');
+      await renderer.loadDesign('../designs/sample-house-design.json');
       buildFloorButtons();
       buildRoomList();
     });