Add Prometheus metrics integration (v0.7.4)

- New Metrics settings tab with enable/disable toggle
- PrometheusController for wp_prometheus_collect_metrics hook
- License gauges: total by status, lifetime, expiring, expiring soon
- Download gauges: total downloads, active versions
- API counters: requests, rate limits, validation errors
- Metric tracking in RestApiController and UpdateController

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

wc-licensed-product.php

@@ -3,7 +3,7 @@
  * Plugin Name: WooCommerce Licensed Product
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wc-licensed-product
  * Description: WooCommerce plugin to sell software products using license keys with domain-based validation.
- * Version: 0.7.3
+ * Version: 0.7.4
  * Author: Marco Graetsch
  * Author URI: https://src.bundespruefstelle.ch/magdev
  * License: GPL-2.0-or-later
@@ -28,7 +28,7 @@ if (!defined('ABSPATH')) {
 }
 
 // Plugin constants
-define('WC_LICENSED_PRODUCT_VERSION', '0.7.3');
+define('WC_LICENSED_PRODUCT_VERSION', '0.7.4');
 define('WC_LICENSED_PRODUCT_PLUGIN_FILE', __FILE__);
 define('WC_LICENSED_PRODUCT_PLUGIN_DIR', plugin_dir_path(__FILE__));
 define('WC_LICENSED_PRODUCT_PLUGIN_URL', plugin_dir_url(__FILE__));