feat: WC-native logging + Add to phpList button on order page

Logging:
- Replace custom file logger with wc_get_logger() (source: woolist-phplist)
- Logs now appear in WooCommerce → Status → Logs, no filesystem access needed
- Remove log viewer / Clear Log from settings page (WC UI handles this)
- Keep "Enable debug logging" checkbox to control DEBUG-level verbosity

Order page meta box:
- New "phpList Sync" side meta box on every order edit page
- Works with both classic (shop_order) and HPOS (woocommerce_page_wc-orders)
- Shows billing email + dropdown of all configured lists
- "Add to phpList" button triggers AJAX subscribe, shows inline result
- Result and full API trace logged to WC logs under woolist-phplist source
- woolist-admin.js handles button state and response display

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

woolist-phplist/assets/js/woolist-admin.js

@@ -0,0 +1,40 @@
+/* global ajaxurl, jQuery */
+( function ( $ ) {
+	'use strict';
+
+	$( document ).on( 'click', '.woolist-manual-subscribe-btn', function () {
+		var $btn  = $( this );
+		var $box  = $btn.closest( '.woolist-metabox-wrap' );
+		var $resp = $box.find( '.woolist-metabox-response' );
+		var listId = $box.find( '.woolist-list-select' ).val();
+
+		$resp.hide().removeClass( 'woolist-mb-success woolist-mb-error' ).html( '' );
+		$btn.prop( 'disabled', true ).text( 'Subscribing\u2026' );
+
+		$.ajax( {
+			url:    ajaxurl,
+			method: 'POST',
+			data:   {
+				action:   'woolist_manual_subscribe',
+				nonce:    $btn.data( 'nonce' ),
+				order_id: $btn.data( 'order-id' ),
+				list_id:  listId,
+			},
+		} )
+		.done( function ( response ) {
+			if ( response.success ) {
+				$resp.addClass( 'woolist-mb-success' ).html( '✓ ' + response.data.message );
+			} else {
+				$resp.addClass( 'woolist-mb-error' ).html( '✗ ' + response.data.message );
+			}
+			$resp.show();
+		} )
+		.fail( function () {
+			$resp.addClass( 'woolist-mb-error' ).html( '✗ Request failed.' ).show();
+		} )
+		.always( function () {
+			$btn.prop( 'disabled', false ).text( 'Add to phpList' );
+		} );
+	} );
+
+} )( jQuery );