feat(fields): 補 3 個 WC runtime usermeta 欄位

wc_last_active / wc_order_count_<prefix> / last_update 先前未註冊，會落回
wp_usermeta。三者皆由 WooCommerce 在 order/session 事件寫入，繁忙商店為高頻。

wc_order_count 走 Users::update_site_user_meta()，key 是
'wc_order_count' . '_' . rtrim( get_blog_prefix(), '_' )；來源外掛寫死主站
形式 'wc_order_count_wp'，multisite 子站（_wp_2）會漏接，這裡改用同一條運算式。

includes/class-tmdo-woocommerce.php

@@ -583,6 +583,27 @@ final class TMDO_WooCommerce {
 					'type'  => 'integer',
 					'label' => 'WC customer last order ID',
 				),
+				// WC runtime stats — written on order/session events, high-frequency
+				// on busy stores. Unregistered they land back in wp_usermeta.
+				array(
+					'key'   => 'wc_last_active',
+					'type'  => 'integer',
+					'label' => 'WC last customer activity timestamp (Unix)',
+				),
+				array(
+					// WooCommerce stores this per-site via Users::update_site_user_meta(),
+					// which appends the de-suffixed blog prefix ('wc_order_count' + '_wp'
+					// on the main site, '_wp_2' on a subsite). Compute it the same way
+					// rather than hardcoding the main-site form.
+					'key'   => 'wc_order_count_' . rtrim( $GLOBALS['wpdb']->get_blog_prefix(), '_' ),
+					'type'  => 'integer',
+					'label' => 'WC order count for the current site (blog-aware key)',
+				),
+				array(
+					'key'   => 'last_update',
+					'type'  => 'integer',
+					'label' => 'WC customer last profile update timestamp (Unix)',
+				),
 			)
 		);
 	}