feat(configurator): server-side surface area calculation from STL

Add trimesh-based surface area calculation for uploaded STL files:
- New /fp/configurator/calculate_surface_area jsonrpc endpoint
- action_calculate_surface_area() method on fp.part.catalog
- "Calculate from 3D Model" button visible when a 3D model is attached
- Returns area in sq in (converted from mm2), vertex/face counts,
  and bounding box dimensions

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

fusion-plating/fusion_plating_configurator/views/fp_part_catalog_views.xml

@@ -44,7 +44,14 @@
                             <field name="geometry_source"/>
                         </group>
                         <group>
-                            <field name="surface_area"/>
+                            <label for="surface_area"/>
+                            <div class="d-flex align-items-center gap-2">
+                                <field name="surface_area" class="oe_inline"/>
+                                <button name="action_calculate_surface_area" type="object"
+                                        string="Calculate from 3D Model"
+                                        class="btn-link" icon="fa-calculator"
+                                        invisible="not model_attachment_id"/>
+                            </div>
                             <field name="surface_area_uom"/>
                             <field name="weight"/>
                         </group>