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/migrations/001_create_oauth_token_cache.sql

@@ -0,0 +1,11 @@
+-- Helpdesk module: OAuth2 token cache (used only when OAuth2 auth mode is active)
+CREATE TABLE IF NOT EXISTS `helpdesk_oauth_token_cache` (
+    `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
+    `tenant_id` INT UNSIGNED NOT NULL,
+    `access_token_encrypted` TEXT NOT NULL,
+    `expires_at` DATETIME NOT NULL,
+    `created_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (`id`),
+    INDEX `idx_helpdesk_oauth_tenant` (`tenant_id`),
+    INDEX `idx_helpdesk_oauth_expires` (`expires_at`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;