moved three.js viewer to static folder

modified upload.html and main.py accordingly

static/upload.html

@@ -22,7 +22,7 @@
   </div>
 
   <script>
-    const API_URL = "http://127.0.0.1:8000/upload";
+    const API_URL = "http://127.0.0.1:8001/upload";
 
     const fileInput = document.getElementById("fileInput");
     const uploadBtn = document.getElementById("uploadBtn");