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_jobs/models/res_users.py

@@ -17,6 +17,15 @@ class ResUsers(models.Model):
              'a different value and saves, it persists here for every '
              'future job and step.',
     )
+    x_fc_signature_image = fields.Binary(
+        string='Plating Signature',
+        attachment=True,
+        help='Drawn or uploaded signature image. Used in WO detail and '
+             'certificate reports for any signature-type prompt this user '
+             'signed off on; falls back to typed initials when blank. '
+             'Capture it once in user preferences; it stamps every '
+             'future sign-off automatically.',
+    )
 
     @api.model
     def _fp_default_initials(self):