feat(certificates): multiple Default CoC Contacts per customer (M2o -> M2m)

res.partner.x_fc_default_coc_contact_id (single Many2one) becomes
x_fc_default_coc_contact_ids (self-referential Many2many 'Default CoC
Contacts') so a customer can list several contacts who need the CoC.

- res.partner: M2m field (rel fp_default_coc_contact_rel) + many2many_tags.
- Cert: contact_partner_id (primary addressee printed on the cert) is set to
  the FIRST CoC contact at job creation + lazy-filled at issue.
- Send: action_send_to_customer pre-fills the email composer with ALL the
  customer's CoC contacts (primary + the rest), falling back to the company.
- fp.job cert-default resolution + the action_issue gate wording updated.
- Migration 19.0.10.2.0: copies each partner's old single value into the new
  M2m, then drops the orphaned column.

Deployed + verified on entech: migration copied 2 existing values, old column
dropped, field is M2m, send pre-fills all contacts. entech-only part_line_ids
/ multi-part resolver preserved.

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

fusion_plating/fusion_plating_certificates/migrations/19.0.10.2.0/post-migrate.py

@@ -0,0 +1,57 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Nexa Systems Inc.
+# License OPL-1
+"""Migrate the single Default CoC Contact (Many2one) to the multi-contact
+Many2many.
+
+The field x_fc_default_coc_contact_id (Many2one column on res_partner) was
+renamed to x_fc_default_coc_contact_ids (self-referential Many2many, rel
+table fp_default_coc_contact_rel). Odoo creates the new rel table during the
+schema-update phase but leaves the old column orphaned. Copy each partner's
+single contact into the new M2m so existing per-customer CoC routing carries
+over, then drop the dead column. Idempotent + guarded on column existence.
+"""
+import logging
+
+_logger = logging.getLogger(__name__)
+
+
+def migrate(cr, version):
+    # Old column still present (Odoo doesn't drop removed-field columns)?
+    cr.execute("""
+        SELECT 1 FROM information_schema.columns
+         WHERE table_name = 'res_partner'
+           AND column_name = 'x_fc_default_coc_contact_id'
+    """)
+    if not cr.fetchone():
+        return
+    # New M2m rel table created by the schema update before this runs.
+    cr.execute("""
+        SELECT 1 FROM information_schema.tables
+         WHERE table_name = 'fp_default_coc_contact_rel'
+    """)
+    if not cr.fetchone():
+        _logger.warning(
+            'fp_default_coc_contact_rel missing — skipping CoC contact '
+            'migration (rel table not created yet).')
+        return
+    # Copy the single value into the M2m (skip rows already present so a
+    # re-run is harmless).
+    cr.execute("""
+        INSERT INTO fp_default_coc_contact_rel (partner_id, contact_id)
+        SELECT p.id, p.x_fc_default_coc_contact_id
+          FROM res_partner p
+         WHERE p.x_fc_default_coc_contact_id IS NOT NULL
+           AND NOT EXISTS (
+               SELECT 1 FROM fp_default_coc_contact_rel r
+                WHERE r.partner_id = p.id
+                  AND r.contact_id = p.x_fc_default_coc_contact_id)
+    """)
+    moved = cr.rowcount
+    cr.execute(
+        "ALTER TABLE res_partner DROP COLUMN IF EXISTS "
+        "x_fc_default_coc_contact_id")
+    _logger.info(
+        'CoC contact migration: copied %s single Default-CoC-Contact value(s) '
+        'into the new x_fc_default_coc_contact_ids M2m, dropped old column.',
+        moved)