feat(helpdesk): align module with core list/drawer standards

- add helpdesk module pages, services, settings and tests

- standardize debtor list on drawer/grid contracts and robust filter drawer behavior

- add helpdesk aside panel navigation and settings visibility provider

- switch primary list slug to helpdesk/debitor and remove helpdesk/search compatibility

- include required core contract updates for list contracts and detail/drawer integration

modules/helpdesk/lib/Module/Helpdesk/Service/HelpdeskOAuthTokenService.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace MintyPHP\Module\Helpdesk\Service;
+
+/**
+ * OAuth2 client_credentials token service for BC OData access.
+ *
+ * This is a skeleton for V1. Basic Auth is the default and recommended
+ * auth mode. OAuth2 support can be activated in settings but the full
+ * token flow (request, cache, refresh) is deferred to a future version.
+ */
+class HelpdeskOAuthTokenService
+{
+    public function __construct(
+        private readonly HelpdeskSettingsGateway $settingsGateway,
+        private readonly HelpdeskTokenRepository $tokenRepository
+    ) {
+    }
+
+    /**
+     * Get a valid access token for BC API calls.
+     *
+     * @return string|null The bearer token, or null if unavailable.
+     */
+    public function getAccessToken(int $tenantId): ?string
+    {
+        if ($this->settingsGateway->getAuthMode() !== HelpdeskSettingsGateway::AUTH_MODE_OAUTH2) {
+            return null;
+        }
+
+        // Check cache first
+        $cached = $this->tokenRepository->findValidToken($tenantId);
+        if ($cached !== null) {
+            return $cached;
+        }
+
+        // Token request would go here in a future version.
+        // For V1, return null to indicate OAuth2 is not yet fully implemented.
+        return null;
+    }
+}