feat(configurator): Three.js 3D viewer for STL files

Add OWL field widget (fp_3d_preview) that renders uploaded STL files
in an interactive 3D viewport:
- Three.js r170 ESM loaded lazily via dynamic import with importmap
- STLLoader + OrbitControls for full model interaction
- Fallback binary STL parser when addon import fails
- Toolbar with wireframe toggle and camera reset
- Vertex/face count display
- Theme-aware SCSS using CSS custom properties and $border-color
- Registered on model_attachment_id in the Part Catalog form

Vendored libs: three.module.min.js (691KB), STLLoader.js, OrbitControls.js

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fusion-plating/fusion_plating_configurator/__manifest__.py

@@ -46,6 +46,13 @@ Provides:
         'views/sale_order_views.xml',
         'views/fp_configurator_menu.xml',
     ],
+    'assets': {
+        'web.assets_backend': [
+            'fusion_plating_configurator/static/src/scss/fp_3d_viewer.scss',
+            'fusion_plating_configurator/static/src/xml/fp_3d_viewer.xml',
+            'fusion_plating_configurator/static/src/js/fp_3d_viewer.js',
+        ],
+    },
     'installable': True,
     'application': False,
     'auto_install': False,