feat(fusion_plating_certificates): add fp.certificate.part child model + ACL

Adds the fp.certificate.part model (one row per part on a combined CoC),
the part_line_ids O2M on fp.certificate, and ACL rows for all three
plating roles. No views yet — Task 2.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_certificates/models/fp_certificate_part.py

@@ -0,0 +1,38 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Nexa Systems Inc.
+# License OPL-1 (Odoo Proprietary License v1.0)
+# Part of the Fusion Plating product family.
+
+from odoo import fields, models
+
+
+class FpCertificatePart(models.Model):
+    """One row per part on a combined Certificate of Conformance.
+
+    A work order can cover several parts that share the same plating
+    process; the combined CoC lists each with its own identity, spec,
+    and quantities. Fields are snapshots taken at cert-creation time.
+    """
+    _name = 'fp.certificate.part'
+    _description = 'Certificate Part Line'
+    _order = 'certificate_id, sequence, id'
+    _rec_name = 'part_number'
+
+    certificate_id = fields.Many2one(
+        'fp.certificate', string='Certificate',
+        required=True, ondelete='cascade', index=True,)
+    sequence = fields.Integer(default=10)
+    sale_order_line_id = fields.Many2one(
+        'sale.order.line', string='Source SO Line',
+        help='The order line this part row was built from (traceability).',)
+    part_catalog_id = fields.Many2one('fp.part.catalog', string='Part')
+    part_number = fields.Char(string='Part Number')      # snapshot
+    part_name = fields.Char(string='Part Name')          # snapshot
+    description = fields.Char(string='Description')        # customer-facing snapshot
+    serial = fields.Char(string='Serial Number(s)')        # comma-joined snapshot
+    customer_spec_id = fields.Many2one(
+        'fusion.plating.customer.spec', string='Customer Spec',)
+    spec_reference = fields.Char(string='Spec Reference')  # snapshot 'CODE Rev X'
+    # Per-part; the parent fp.certificate keeps cert-level legacy totals.
+    quantity_shipped = fields.Integer(string='Qty Shipped')
+    nc_quantity = fields.Integer(string='NC Qty')