fix: remove type=module from scripts — breaks THREE global in UMD build

Three.js UMD uses 'this' to set window.THREE, but module scope has
this===undefined. Changed to regular scripts. Added visible error if
THREE fails to load.

studio.py

@@ -65,9 +65,15 @@ body {{ background: #1a1a2e; overflow: hidden; font-family: 'Courier New', monos
   <div id="phase-progress"><div id="phase-fill" style="width:0%"></div></div>
 </div>
 
-<script src="{_THREEJS_CDN}" type="module"></script>
+<script src="{_THREEJS_CDN}"></script>
 <script src="{_CHARACTERS_JS_URL}"></script>
-<script type="module">
+<script>
+if (typeof THREE === 'undefined') {{
+  document.body.innerHTML = '<div style="color:#f66;padding:2rem;font-family:monospace">'
+    + 'ERROR: Three.js failed to load from CDN.<br>'
+    + 'URL: {_THREEJS_CDN}</div>';
+  throw new Error('THREE is undefined');
+}}
 const assignments = {assignments_json};
 
 const DESK_POSITIONS = [