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/models/fp_part_catalog.py

@@ -3,7 +3,7 @@
 # License OPL-1 (Odoo Proprietary License v1.0)
 # Part of the Fusion Plating product family.
 
-from odoo import fields, models
+from odoo import api, fields, models, _
 
 
 class FpPartCatalog(models.Model):
@@ -63,3 +63,39 @@ class FpPartCatalog(models.Model):
         ('fp_part_catalog_partner_partnum_uniq', 'unique(partner_id, part_number)',
          'Part number must be unique per customer.'),
     ]
+
+    def action_calculate_surface_area(self):
+        """Calculate surface area from the uploaded 3D model file."""
+        self.ensure_one()
+        if not self.model_attachment_id:
+            from odoo.exceptions import UserError
+            raise UserError(_('No 3D model file uploaded.'))
+
+        try:
+            import trimesh
+        except ImportError:
+            from odoo.exceptions import UserError
+            raise UserError(_('trimesh library not installed on the server. Contact your administrator.'))
+
+        import base64
+        import io
+
+        raw = base64.b64decode(self.model_attachment_id.datas)
+        mesh = trimesh.load(io.BytesIO(raw), file_type='stl')
+        area_mm2 = mesh.area
+        area_sqin = area_mm2 / 645.16
+
+        self.surface_area = round(area_sqin, 4)
+        self.surface_area_uom = 'sq_in'
+        self.geometry_source = '3d_model'
+
+        return {
+            'type': 'ir.actions.client',
+            'tag': 'display_notification',
+            'params': {
+                'title': _('Surface Area Calculated'),
+                'message': _('%.4f sq in (%.2f mm\u00b2) from %d faces') % (area_sqin, area_mm2, len(mesh.faces)),
+                'type': 'success',
+                'sticky': False,
+            },
+        }