[IMP] stock_picking_batch_custom: order detailed ops by category, product, partner

Store picking_partner_id on stock.move.line and set default_order to
product_categ_id, product_id, picking_partner_id in the detailed operations view.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

stock_picking_batch_custom/models/stock_move_line.py

@@ -23,6 +23,12 @@ class StockMoveLine(models.Model):
         readonly=True,
     )
 
+    picking_partner_id = fields.Many2one(
+        related="picking_id.partner_id",
+        store=True,
+        readonly=True,
+    )
+
     is_collected = fields.Boolean(
         string="Collected",
         default=False,