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-att-consent.php

@@ -33,6 +33,7 @@ class ATT_Consent {
 		'consent_expiry'         => 365,
 		'floating_widget'        => 'bottom-right',
 		'floating_widget_label'  => 'Cookie Settings',
+		'expose_gtag_global'     => false,
 
 		// Appearance.
 		'banner_bg_color'       => '#1a1a2e',