fix(plating): CoC signer follows Settings "Certificate Owner" (no stale freeze)

Changing Settings -> Certificate Owner didn't move existing certs: the signer
was snapshotted from the company owner at cert-creation time, and the CoC
prefers that snapshot over the live owner.

- _fp_create_certificates no longer freezes the company owner into
  certified_by_id; it snapshots ONLY a deliberate per-spec signer. Empty
  certified_by_id then resolves the LIVE company owner in the CoC report.
- action_issue lazy-fill made robust: resolves the company via the SO /
  env.company (fp.certificate has no company_id) so it fills the CURRENT
  owner at issue and the "Certified By" gate still passes.
- Settings help text corrected: signature comes from the user's Plating
  Signature (Preferences -> My Profile), not "HR Employee".
- Data fix on entech: cleared certified_by_id on 5 stale draft CoCs with no
  per-spec signer so they follow the current owner.

Bump certificates 19.0.9.3.0, jobs 19.0.11.4.0. Verified: CoC-30058 resolves
signer = Garry Singh (has Plating Signature), renders clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

fusion_plating/fusion_plating_certificates/__manifest__.py

@@ -5,7 +5,7 @@
 
 {
     'name': 'Fusion Plating — Certificates',
-    'version': '19.0.9.2.0',
+    'version': '19.0.9.3.0',
     'category': 'Manufacturing/Plating',
     'summary': 'Certificate registry for CoC, thickness reports, and quality documents.',
     'description': """