refactor(fusion_helpdesk): owner contact is a res.partner, not two text fields

Smaller UX simplification on the client side: the owner is already a
contact in entech's address book, so picking one is faster + safer than
re-typing their email and name (and avoids typos creeping into the
approval-email To: header).

What changed:
- Entech settings: drop fhd_owner_email + fhd_owner_name char fields;
  add fhd_owner_partner_id Many2one to res.partner exposed in the
  same "Owner Approval" block as a single partner selector. Quick-create
  + create-and-edit kept enabled so admins can spin up a new partner
  inline if the owner isn't already in the system.
- controllers/main.py::_read_config: derives owner_email + owner_name
  from the selected partner via the new _resolve_owner_contact helper.
  Missing / dangling partner id → blank email + name → central simply
  won't see the keys and the Engage button stays disabled (correct
  "not configured" behaviour).
- Nexa side: ZERO changes. Still receives owner_email + owner_name
  strings on the ticket payload, still upserts client_key.owner_email/
  name. The partner abstraction stops at the entech boundary.
- migrations/19.0.2.1.0/post-migration.py auto-resolves the legacy
  fusion_helpdesk.owner_email ICP value to an existing res.partner
  (lowest-id match on lowercased email), writes the new
  fusion_helpdesk.owner_partner_id key, and deletes the obsolete
  owner_email + owner_name ICP rows so a future reader doesn't trip
  over stale config.

Verified live on entech: kris@enplating.ca → res.partner #2308 ("Kris
Pathinather"), legacy keys purged, controller._resolve_owner_contact
returns the expected (email, name). The piggyback payload is unchanged
so existing client_key sync continues to work without a central
redeploy.

Bumps fusion_helpdesk to 19.0.2.1.0. fusion_helpdesk_central stays at
19.0.2.0.0 (no central-side changes required).

fusion_helpdesk/controllers/main.py

@@ -228,12 +228,29 @@ class FusionHelpdeskController(http.Controller):
             'client_label': (
                 ICP.get_param('fusion_helpdesk.client_label') or ''
             ).strip(),
-            'owner_email': (
-                ICP.get_param('fusion_helpdesk.owner_email') or ''
-            ).strip(),
-            'owner_name': (
-                ICP.get_param('fusion_helpdesk.owner_name') or ''
-            ).strip(),
+            # Owner contact is configured as a res.partner reference; we
+            # derive email + name on read so the rest of the submit path
+            # doesn't have to know about the partner. Missing / dangling
+            # partner id → blank email + name → central simply won't see
+            # the keys and the Engage button stays disabled (which is the
+            # correct "not configured" behaviour).
+            **self._resolve_owner_contact(ICP),
+        }
+
+    def _resolve_owner_contact(self, ICP):
+        raw = (ICP.get_param('fusion_helpdesk.owner_partner_id') or '').strip()
+        try:
+            partner_id = int(raw)
+        except (TypeError, ValueError):
+            return {'owner_email': '', 'owner_name': ''}
+        if partner_id <= 0:
+            return {'owner_email': '', 'owner_name': ''}
+        partner = request.env['res.partner'].sudo().browse(partner_id).exists()
+        if not partner:
+            return {'owner_email': '', 'owner_name': ''}
+        return {
+            'owner_email': (partner.email or '').strip(),
+            'owner_name': (partner.name or '').strip(),
         }
 
     def _authenticate(self, cfg):