Rename viewer bundles .js -> .mjs so they stop leaking into the main realm

ComfyUI auto-imports every web/**/*.js into the shared main page; the four
big bundles (three, vtk-gltf, viewer-bundle-vtk, gsplat) only ever run
inside the viewer iframes but were getting pulled into the main document
too, where they wrote window.THREE / window.vtk / globalThis.* and could
collide with any other 3D pack. The **/*.js glob only matches .js, so
renaming to .mjs drops them from the auto-import while the iframes still
load them via classic <script src> (mime resolves to text/javascript).
window.* pollution from these bundles is gone from the main realm.

javascript/viewer_fbx_debug.html

@@ -439,7 +439,7 @@
             }
 
             var bundleScript = document.createElement('script');
-            bundleScript.src = baseUrl + 'js/viewer-bundle-three.js';
+            bundleScript.src = baseUrl + 'js/viewer-bundle-three.mjs';
             bundleScript.onload = function() {
                 console.log('[FBX Debug Viewer] Three.js bundle loaded from:', bundleScript.src);
                 initViewer();