feat(helpdesk): add Domains list page with BC OData contract type enrichment

Add a new "Domains" page to the helpdesk module that fetches domain data
from the FS_Contract_Domains OData endpoint and enriches each domain with
its contract type (PI_Header_Type) by joining with FS_Contract_Lines_Test
where Type = 'Domain'.

New files:
- domains/index().php, index(default).phtml, filter-schema.php — list page
- domains-data().php — data endpoint with PHP-side filtering/sorting
- helpdesk-domains-index.js — Grid.js via initStandardListPage()

Gateway additions:
- listDomains() — fetch all contract domains
- listDomainContractLines() — fetch domain-type contract lines for type lookup

Sidebar restructured into three collapsible groups (Lookup, Monitoring,
Administration) with per-group icons and color coding, matching the core
admin panel pattern.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/helpdesk/module.php

@@ -15,6 +15,8 @@ return [
 
     'routes' => [
         ['path' => 'helpdesk/search-data', 'target' => 'helpdesk/search-data'],
+        ['path' => 'helpdesk/domains', 'target' => 'helpdesk/domains'],
+        ['path' => 'helpdesk/domains-data', 'target' => 'helpdesk/domains-data'],
         ['path' => 'helpdesk/debitor/{id}', 'target' => 'helpdesk/debitor'],
         ['path' => 'helpdesk/ticket/{id}', 'target' => 'helpdesk/ticket'],
         ['path' => 'helpdesk/settings', 'target' => 'helpdesk/settings'],