feat(updates): wire PUC v5 registration into Plugin::boot()

register_update_checker() guards on is_file + class_exists so the plugin
degrades cleanly on installs that ship without the vendored lib (no update
notices, but plugin core remains functional).

includes/class-plugin.php

@@ -50,10 +50,30 @@ final class Plugin
         Dispatcher::register_hooks();
         (new CF7Source())->register();
 
+        self::register_update_checker();
+
         // Admin
         if (is_admin()) {
             (new Settings_Page())->register();
             (new Dashboard_Widget())->register();
         }
     }
+
+    private static function register_update_checker(): void
+    {
+        $loader = CF7STG_PLUGIN_DIR . 'includes/lib/plugin-update-checker/plugin-update-checker.php';
+        if (!is_file($loader)) {
+            return;
+        }
+        require_once $loader;
+        if (!class_exists('YahnisElsts\\PluginUpdateChecker\\v5\\PucFactory')) {
+            return;
+        }
+
+        \YahnisElsts\PluginUpdateChecker\v5\PucFactory::buildUpdateChecker(
+            'https://git.netranking.ru/bryzgalov/cf7-spam-to-telegram/raw/branch/main/wp-plugin-info.json',
+            CF7STG_PLUGIN_FILE,
+            'cf7-spam-to-telegram'
+        );
+    }
 }