feat(numbering): wire CoC/RCV/DLV/PU into parent-numbered mixin + rename counters

Per-model counter fields on sale.order renamed to x_fc_pn_*_count
to avoid collision with pre-existing compute fields of the same
short name in bridge_mrp / receiving / configurator (silent
compute-override was suppressing the storage). 4 child models
(fp.certificate, fp.receiving, fusion.plating.delivery,
fusion.plating.pickup.request) now derive names as PFX-<parent>
with -NN suffix from the 2nd onward.

fusion.plating.pickup.request gains a sale_order_id field
(optional) so pickups created against an SO get parent-derived
names, while standalone pickups (pre-SO) fall back to PU/YYYY/NNNN.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating/models/fp_job.py

@@ -399,7 +399,7 @@ class FpJob(models.Model):
         return 'WO'
 
     def _fp_parent_counter_field(self):
-        return 'x_fc_wo_count'
+        return 'x_fc_pn_wo_count'
 
     @api.model_create_multi
     def create(self, vals_list):