feat(configurator): SO-create applies one tax to all lines + typed charge line

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

fusion_plating/fusion_plating_configurator/models/sale_order_line.py

@@ -326,6 +326,9 @@ class SaleOrderLine(models.Model):
              'pair, falling back to the part\'s default range. Prints '
              'verbatim on the cert, packing slip, and invoice.',
     )
+    x_fc_is_lot_priced = fields.Boolean(string='Lot Priced')
+    x_fc_lot_total = fields.Monetary(
+        string='Lot Total', currency_field='currency_id')
 
     # ---- Express Orders per-line flags (2026-05-26) ----
     # Mirror fp.direct.order.line.{customer_line_ref, masking_enabled, bake_instructions}