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/__init__.py

@@ -5,6 +5,7 @@
 
 from . import fp_thickness_reading
 from . import fp_certificate
+from . import fp_certificate_part
 from . import res_config_settings
 from . import res_partner
 from . import fp_delivery