feat: initial WooCow plugin — Mailcow/WooCommerce integration

- Mailcow API client wrapping domains, mailboxes, aliases endpoints
- Admin backend: server management, customer-domain assignments, mailbox overview
- WooCommerce My Account: email hosting tab with mailbox/alias management
- Per-mailbox password change (independent of WP account password)
- Optional WP account password sync to all customer mailboxes
- Installer creates wp_woocow_servers and wp_woocow_assignments DB tables
- Full nonce + capability + ownership verification on all AJAX endpoints

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

woocow.php

@@ -0,0 +1,41 @@
+<?php
+/**
+ * Plugin Name: WooCow
+ * Description: Mailcow email hosting management for WooCommerce customers.
+ * Version:     1.0.0
+ * Author:      WooCow
+ * Text Domain: woocow
+ * Requires at least: 6.2
+ * Requires PHP: 8.1
+ * WC requires at least: 7.0
+ */
+
+defined( 'ABSPATH' ) || exit;
+
+define( 'WOOCOW_VERSION',     '1.0.0' );
+define( 'WOOCOW_PLUGIN_FILE', __FILE__ );
+define( 'WOOCOW_PLUGIN_DIR',  plugin_dir_path( __FILE__ ) );
+define( 'WOOCOW_PLUGIN_URL',  plugin_dir_url( __FILE__ ) );
+
+require_once WOOCOW_PLUGIN_DIR . 'includes/class-woocow-installer.php';
+require_once WOOCOW_PLUGIN_DIR . 'includes/class-woocow-api.php';
+require_once WOOCOW_PLUGIN_DIR . 'includes/class-woocow-admin.php';
+require_once WOOCOW_PLUGIN_DIR . 'includes/class-woocow-account.php';
+require_once WOOCOW_PLUGIN_DIR . 'includes/class-woocow-pw-sync.php';
+
+register_activation_hook( __FILE__, [ 'WooCow_Installer', 'install' ] );
+
+add_action( 'plugins_loaded', function () {
+    if ( ! class_exists( 'WooCommerce' ) ) {
+        add_action( 'admin_notices', function () {
+            printf(
+                '<div class="notice notice-error"><p>%s</p></div>',
+                esc_html__( 'WooCow requires WooCommerce to be installed and active.', 'woocow' )
+            );
+        } );
+        return;
+    }
+    new WooCow_Admin();
+    new WooCow_Account();
+    new WooCow_PW_Sync();
+} );