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/web/js/helpdesk-settings.js

@@ -0,0 +1,77 @@
+/**
+ * Helpdesk settings page — auth mode toggle and connection test.
+ */
+
+// Toggle OAuth2 vs Basic Auth field visibility
+const authModeSelect = document.getElementById('auth_mode');
+const basicFields = document.getElementById('helpdesk-basic-auth-fields');
+const oauth2Fields = document.getElementById('helpdesk-oauth2-fields');
+
+const toggleAuthFields = () => {
+  if (!authModeSelect || !basicFields || !oauth2Fields) {
+    return;
+  }
+  const isOAuth2 = authModeSelect.value === 'oauth2';
+  basicFields.style.display = isOAuth2 ? 'none' : '';
+  oauth2Fields.style.display = isOAuth2 ? '' : 'none';
+};
+
+if (authModeSelect) {
+  authModeSelect.addEventListener('change', toggleAuthFields);
+  toggleAuthFields();
+}
+
+// Connection test button
+const testButton = document.getElementById('helpdesk-test-connection-button');
+const testResult = document.getElementById('helpdesk-test-connection-result');
+
+if (testButton && testResult) {
+  testButton.addEventListener('click', async () => {
+    testButton.disabled = true;
+    testResult.textContent = testButton.dataset.testingLabel || 'Testing...';
+    testResult.className = '';
+
+    try {
+      const csrfMeta = document.querySelector('meta[name="csrf-token"]');
+      const csrfInput = document.querySelector('input[name="csrf_token"]');
+      const csrfToken = csrfInput?.value || csrfMeta?.content || '';
+
+      const formData = new FormData();
+      if (csrfToken) {
+        formData.append('csrf_token', csrfToken);
+      }
+
+      const response = await fetch(
+        new URL('helpdesk/settings/test-connection-data', document.baseURI).href,
+        {
+          method: 'POST',
+          body: formData,
+          credentials: 'same-origin',
+        },
+      );
+
+      const data = await response.json();
+
+      if (data.ok) {
+        testResult.textContent = data.message || 'Connection successful';
+        testResult.style.color = 'var(--color-success, green)';
+      } else {
+        let msg = data.error || 'Connection failed';
+        if (data.debug?.url) {
+          msg += '\nURL: ' + data.debug.url;
+        }
+        if (data.debug?.http_code) {
+          msg += ' (HTTP ' + data.debug.http_code + ')';
+        }
+        testResult.textContent = msg;
+        testResult.style.color = 'var(--color-error, red)';
+        testResult.style.whiteSpace = 'pre-wrap';
+      }
+    } catch {
+      testResult.textContent = 'Connection failed';
+      testResult.style.color = 'var(--color-error, red)';
+    } finally {
+      testButton.disabled = false;
+    }
+  });
+}