fix: Defer textdomain loading to init action for WordPress 6.7+ compatibility (v0.4.8)

Fixes _load_textdomain_just_in_time notice and headers already sent warnings
on admin pages by deferring load_plugin_textdomain() and Settings tab label
initialization to the init action instead of plugins_loaded.

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

wp-prometheus.php

@@ -3,7 +3,7 @@
  * Plugin Name: WP Prometheus
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wp-prometheus
  * Description: Prometheus metrics endpoint for WordPress with extensible hooks for custom metrics.
- * Version: 0.4.7
+ * Version: 0.4.8
  * Requires at least: 6.4
  * Requires PHP: 8.3
  * Author: Marco Graetsch
@@ -169,7 +169,7 @@ wp_prometheus_early_metrics_check();
  *
  * @var string
  */
-define( 'WP_PROMETHEUS_VERSION', '0.4.7' );
+define( 'WP_PROMETHEUS_VERSION', '0.4.8' );
 
 /**
  * Plugin file path.