Add optional global gtag() exposure setting

New checkbox in General settings to conditionally expose window.gtag()
for compatibility with third-party scripts (e.g. HFCM). Defaults to
off, keeping only window.attCCGtag() available.

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

includes/class-frontend.php

@@ -72,6 +72,9 @@ var c=window.attCCConfig;
 window.dataLayer=window.dataLayer||[];
 function g(){window.dataLayer.push(arguments);}
 window.attCCGtag=g;
+<?php if ( ! empty( $s['expose_gtag_global'] ) ) : ?>
+window.gtag=g;
+<?php endif; ?>
 g('js',new Date());
 if(c.ads_data_redaction){g('set','ads_data_redaction',true);}
 if(c.url_passthrough){g('set','url_passthrough',true);}