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/models/fp_job.py

@@ -262,6 +262,33 @@ class FpJob(models.Model):
     # Header counters mirror the paper traveller's "Qty Rec." / "VIS INSP."
     # / "Rework" columns (screens 16-18). Sub 12c's traveller report pulls
     # these into the printed header.
+    # ---- Customer references mirrored from sale.order ----------------
+    # Populated on SO confirm by _fp_auto_create_job. Without these
+    # mirrors, certs / deliveries / chatter would have to round-trip
+    # through job.sale_order_id.x_fc_* to find the customer's references,
+    # and offline-printed paperwork on the shop floor wouldn't show them.
+    x_fc_customer_job_number = fields.Char(
+        string='Customer Job #',
+        tracking=True,
+        help='Customer\'s own job/lot reference. Copied from the '
+             'sale order when the job is auto-created on SO confirm; '
+             'printed on the cert, traveller, and BoL.',
+    )
+    x_fc_po_number = fields.Char(
+        string='Customer PO #',
+        tracking=True,
+        help='Customer purchase order number. Mirrored from sale.order '
+             'so the shop floor and printed paperwork have it without '
+             'a round-trip to the SO.',
+    )
+    x_fc_rush_order = fields.Boolean(
+        string='Rush Order',
+        tracking=True,
+        help='High-priority flag mirrored from sale.order. Operators see '
+             'this on the queue / tablet at-a-glance — saves lifting the '
+             'job form to know it\'s rush.',
+    )
+
     qty_received = fields.Integer(
         string='Qty Received',
         help='Paper traveller "Qty Rec." column.',