Guard lt.* calls when base.js unavailable to prevent crash

Wraps all lt.keys.initDefaults() calls in `if (window.lt)` guards across
6 view files. Adds `if (!window.lt) return` bail-out in keyboard-shortcuts.js
and `if (window.lt)` guard in settings.js DOMContentLoaded handler.

This prevents TypeError crashes when /web_template/base.js returns 404,
which was causing the admin menu click delegation to never register.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

views/admin/CustomFieldsView.php

@@ -204,7 +204,7 @@ $nonce = SecurityHeadersMiddleware::getNonce();
             saveField(e);
         });
 
-        lt.keys.initDefaults();
+        if (window.lt) lt.keys.initDefaults();
 
         function toggleOptionsField() {
             const type = document.getElementById('field_type').value;