feat(jobs): persist Customer Job # + PO # + Rush Order on fp.job

Tier 1 of the SO->fp.job persistence audit. Three customer-reference
fields entered on sale.order's Plating tab were not flowing through
to fp.job (or SO lines), so the shop floor and printed paperwork
(traveller, BoL, cert) had to round-trip via sale_order_id every time.

Changes:
- fp.job: new x_fc_customer_job_number (Char, tracking), x_fc_po_number
  (Char, tracking), x_fc_rush_order (Boolean, tracking). All three
  populated by _fp_auto_create_job at SO confirm time.
- sale.order.line: x_fc_customer_job_number / x_fc_po_number added as
  stored related fields off order_id so per-line list views show the
  customer's references without navigating to the order header
  (x_fc_rush_order was already on lines).
- fp.job form view: small Customer References group under the title
  surfaces the three fields where the user expects them.

Verified end-to-end: SO -> SO line related fields -> fp.job direct
fields all carry the same value.

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

fusion_plating/fusion_plating/__manifest__.py

@@ -5,7 +5,7 @@
 
 {
     'name': 'Fusion Plating',
-    'version': '19.0.18.15.5',
+    'version': '19.0.18.15.6',
     'category': 'Manufacturing/Plating',
     'summary': 'Core plating / metal finishing ERP: facilities, processes, tanks, baths, jobs, operators.',
     'description': """