fix(#60): Corregir error en creación de actividades al rechazar muestra

- Agregar campo obligatorio res_model_id en mail.activity
- Obtener ID del modelo stock.lot antes de crear actividad
- Prevenir error de validación al rechazar muestras

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

lims_management/models/stock_lot.py

@@ -490,10 +490,14 @@ class StockLot(models.Model):
         if receptionist_group:
             receptionist_users = receptionist_group.users
             
+            # Get the model id for stock.lot
+            model_id = self.env['ir.model'].search([('model', '=', 'stock.lot')], limit=1).id
+            
             # Create activities for receptionists
             for user in receptionist_users:
                 self.env['mail.activity'].create({
                     'res_model': 'stock.lot',
+                    'res_model_id': model_id,  # Campo obligatorio
                     'res_id': resample.id,
                     'activity_type_id': self.env.ref('mail.mail_activity_data_todo').id,
                     'summary': _('Nueva re-muestra pendiente de recolección'),