feat(plating): close 6 compliance gaps from required-fields audit

Following the workforce-E2E + required-fields audit, ship the first 6
high-priority gates so critical workflow + compliance fields can no
longer be left empty by accident.

**1. Invoice payment terms (account.move)**
- create() now auto-inherits `invoice_payment_term_id` from
  partner.property_payment_term_id when missing
- action_post() raises UserError if still missing — accountant must
  pick one before posting (prevents silent "immediate" due-date)

**2. MO facility (mrp.production)**
- action_confirm() auto-derives `x_fc_facility_id` if unset, in order:
  SO override → res.company.x_fc_default_facility_id → first active
  facility — then HARD GATES: raises UserError if still empty.
  Without facility every downstream record (WO, batch, bath log,
  cert) is missing the "where" half of the audit trail.

**3. WO facility (mrp.workorder)**
- Switched `x_fc_facility_id` from related (workcenter only) to a
  proper compute that falls back to production_id.x_fc_facility_id.
  Stub workcenters auto-created from process node names usually have
  no facility — the MO always does (from #2 above).

**4. Thickness reading calibration_std (fp.thickness.reading)**
- `calibration_std_ref` is now `required=True` with sensible default
  ("NiP/Al STD SET SN 100174568"). Nadcap mandates which calibration
  standard the gauge was checked against — without it the cert
  data has no chain back to a metrology record.

**5. Delivery POD gate (fusion.plating.delivery)**
- action_mark_delivered() raises UserError if no `pod_id`. Driver
  must capture POD on the iPad (recipient signature + photos +
  notes) BEFORE marking delivered. Without POD there's no signed
  receipt to back the invoice or defend a delivery dispute.

**6. Certificate spec_reference gate (fp.certificate)**
- action_issue() raises UserError if no `spec_reference`. The cert
  ATTESTS to a spec — leaving it blank produces a piece of paper
  that AS9100 / Nadcap auditors will (rightfully) reject.

**Simulator updated**: scripts/fp_e2e_workforce.py
- Sets net-30 on the test customer + ensures a default facility
- New PHASE 4c: 5 negative tests (one per new gate), each wrapped
  in a SAVEPOINT so SQL constraint violations don't abort the txn
- Driver now creates POD on iPad BEFORE marking delivered

**Final E2E**: 48 PASS / 2 WARN / 0 FAIL out of 50 checks.
The 2 remaining WARNs (bake-window auto-create, first-piece gate)
are expected behaviour — both are coating-driven and the test
coating intentionally doesn't trigger them.

All 7 negative tests now pass:
  ✓ Test 1: WO start without operator → blocked
  ✓ Test 2: WO start on wet WO without bath/tank → blocked
  ✓ Test 3: MO confirm without facility → blocked
  ✓ Test 4: Cert issue without spec_reference → blocked
  ✓ Test 5: Delivery delivered without POD → blocked
  ✓ Test 6: Invoice post without payment terms → blocked
  ✓ Test 7: Thickness reading without cal std → blocked (DB NOT NULL)

Audit script (scripts/fp_required_fields_audit.py) committed too —
it's the diagnostic that surfaced these gaps and can be re-run to
catch new ones.

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

fusion_plating/fusion_plating_certificates/__manifest__.py

@@ -5,7 +5,7 @@
 
 {
     'name': 'Fusion Plating — Certificates',
-    'version': '19.0.3.0.0',
+    'version': '19.0.3.1.0',
     'category': 'Manufacturing/Plating',
     'summary': 'Certificate registry for CoC, thickness reports, and quality documents.',
     'description': """

fusion_plating/fusion_plating_certificates/models/fp_certificate.py

@@ -267,6 +267,16 @@ class FpCertificate(models.Model):
         for rec in self:
             if rec.state != 'draft':
                 raise UserError(_('Only draft certificates can be issued.'))
+            # Spec reference is what the cert ATTESTS — without it the
+            # cert is just a piece of paper. AS9100 / Nadcap require
+            # naming the spec the work was performed to.
+            if not rec.spec_reference:
+                raise UserError(_(
+                    'Cannot issue certificate "%(name)s" — no Spec '
+                    'Reference set.\n\nFill the Spec Reference field '
+                    '(e.g. "AMS 2404", "MIL-C-26074") so the cert '
+                    'states which standard the work meets.'
+                ) % {'name': rec.name or rec.display_name})
             rec.state = 'issued'
             rec.message_post(body=_('Certificate issued.'))
 

fusion_plating/fusion_plating_certificates/models/fp_thickness_reading.py

@@ -45,7 +45,13 @@ class FpThicknessReading(models.Model):
         string='Product Ref', help='e.g. "2805031 / NiP/Al-alloys 2805030"',
     )
     calibration_std_ref = fields.Char(
-        string='Calibration Std', help='e.g. "NiP/Al STD SET SN 100174568"',
+        string='Calibration Std',
+        required=True,
+        default='NiP/Al STD SET SN 100174568',
+        help='Nadcap mandatory: which calibration standard the gauge '
+             'was checked against. Defaults to the shop\'s primary '
+             'standard but should be overridden if a different std '
+             'was used for this reading.',
     )
     microscope_image_id = fields.Many2one(
         'ir.attachment', string='Microscope Image',