Improve cross-domain tracking and add "Always" script category

Move linker config into gtag('config') call with accept_incoming and
decorate_forms for reliable cross-domain linking. Capture _gl parameter
in sessionStorage to preserve attribution across navigation. Add
referrer-based attribution replay fallback so GA4 reports source/medium
instead of (not set) when UTMs are absent. Add "Always" script category
that executes without waiting for consent.

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

admin/views/settings-scripts.php

@@ -82,11 +82,12 @@ $scripts = ATT_Consent_Scripts_Manager::get_all_scripts();
 						<th><label for="att-cc-script-category"><?php esc_html_e( 'Category', 'att-consent' ); ?></label></th>
 						<td>
 							<select id="att-cc-script-category" name="category">
+								<option value="always"><?php esc_html_e( 'Always', 'att-consent' ); ?></option>
 								<option value="functional"><?php esc_html_e( 'Functional', 'att-consent' ); ?></option>
 								<option value="analytics" selected><?php esc_html_e( 'Analytics', 'att-consent' ); ?></option>
 								<option value="marketing"><?php esc_html_e( 'Marketing', 'att-consent' ); ?></option>
 							</select>
-							<p class="description"><?php esc_html_e( 'The script will only execute after the visitor consents to this category.', 'att-consent' ); ?></p>
+							<p class="description"><?php esc_html_e( '"Always" scripts run on every page load without waiting for consent. Other categories execute only after the visitor consents.', 'att-consent' ); ?></p>
 						</td>
 					</tr>
 					<tr>