feat: "Lizenz upgraden" oeffnet vorausgefuellte mail (v1.5.4)

Button im Lizenz-tab (status "Plaetze belegt") oeffnet jetzt einen mailto-link
an info@lucas-orth.de, Betreff "Lizenzupgrade", body mit leeren feldern
"Lizenzkey:" und "Bestellmail:" zum ausfuellen (key NICHT vorausgefuellt).

+ i18n DE/EN. version 1.5.4.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

gdpr-content-blocker/includes/class-license.php

@@ -371,9 +371,18 @@ class CB_License {
 		</tbody></table>
 
 		<?php if ( $status === 'limit' ) : ?>
-			<!-- Not enough seats to activate this site: offer an upgrade. -->
+			<?php
+			// Upgrade = open a pre-addressed e-mail with empty fields to fill in.
+			$mail_subject = rawurlencode( __( 'Lizenzupgrade', 'gdpr-content-blocker' ) );
+			$mail_body    = rawurlencode(
+				__( 'Lizenzkey:', 'gdpr-content-blocker' ) . " \r\n"
+				. __( 'Bestellmail:', 'gdpr-content-blocker' ) . ' '
+			);
+			$mailto = 'mailto:info@lucas-orth.de?subject=' . $mail_subject . '&body=' . $mail_body;
+			?>
+			<!-- Not enough seats to activate this site: offer an upgrade by e-mail. -->
 			<p style="margin:8px 0 16px;">
-				<a href="https://lucas-orth.de/wp-plugins/gdpr-content-blocker/" target="_blank" rel="noopener noreferrer" class="button button-primary">
+				<a href="<?php echo esc_url( $mailto ); ?>" class="button button-primary">
 					<?php esc_html_e( 'Lizenz upgraden', 'gdpr-content-blocker' ); ?>
 				</a>
 				<span class="description" style="margin-left:8px;">