feat(fusion_helpdesk_central): expose OpenAI key + cron settings in UI

Adding the 'Fusion Helpdesk Central' block to General Settings so the
three ICP keys the engagement flow reads are configurable from a real
form instead of forcing admins to open Technical → System Parameters.

Three settings, all wired via config_parameter= so the existing read
paths (engagement_wizard, _fc_send_engagement_reminders) keep working
unchanged:

- fusion_helpdesk_central.openai_api_key (password widget — doesn't
  render plaintext on the form)
- fusion_helpdesk_central.openai_model (default 'gpt-4o-mini')
- fusion_helpdesk_central.engagement_reminder_days (default 3, 0
  disables the reminder cron entirely)

Bumps fusion_helpdesk_central to 19.0.2.2.0.

Find under Settings → Fusion Helpdesk Central. The block has two
sub-sections: "Owner Approval — AI Summary" (key + model) and
"Owner Approval — Reminder Cadence" (days).

fusion_helpdesk_central/__manifest__.py

@@ -3,7 +3,7 @@
 # License OPL-1
 {
     'name': 'Fusion Helpdesk Central — Client API Keys',
-    'version': '19.0.2.1.0',
+    'version': '19.0.2.2.0',
     'category': 'Productivity',
     'summary': 'Admin UI on the central Odoo for issuing per-client API '
                'keys used by fusion_helpdesk client deployments.',
@@ -37,6 +37,7 @@ Depends only on `helpdesk`. No client-side install needed.
         'views/engagement_wizard_views.xml',
         'views/engagement_reporting_views.xml',
         'views/portal_templates.xml',
+        'views/res_config_settings_views.xml',
     ],
     'installable': True,
     'auto_install': False,