feat(admin): dashboard widget shown only when there are failed queue items

admin/class-dashboard-widget.php

@@ -0,0 +1,30 @@
+<?php
+declare(strict_types=1);
+
+namespace Cf7stg;
+
+final class Dashboard_Widget
+{
+    public function register(): void
+    {
+        add_action('wp_dashboard_setup', [$this, 'maybe_register_widget']);
+    }
+
+    public function maybe_register_widget(): void
+    {
+        if (Queue::count_failed() === 0) return;
+        wp_add_dashboard_widget(
+            'cf7stg_dashboard_errors',
+            '⚠️ CF7 Spam → Telegram: ошибки доставки',
+            [$this, 'render']
+        );
+    }
+
+    public function render(): void
+    {
+        $failed = Queue::list_failed(10);
+        $count = Queue::count_failed();
+        $settings_url = admin_url('options-general.php?page=cf7stg-settings');
+        include CF7STG_PLUGIN_DIR . 'admin/views/dashboard-widget.php';
+    }
+}

admin/views/dashboard-widget.php

@@ -0,0 +1,15 @@
+<?php
+/** @var array<int,object> $failed */
+/** @var int $count */
+/** @var string $settings_url */
+?>
+<p>Есть <b><?php echo (int)$count; ?></b> неотправленных сообщений (TG-API отвечает ошибкой):</p>
+<ul style="margin:0 0 8px 18px;list-style:disc">
+<?php foreach ($failed as $row): ?>
+    <li>
+        <?php echo esc_html((string)$row->created_at); ?> —
+        <?php echo esc_html((string)$row->last_error); ?>
+    </li>
+<?php endforeach; ?>
+</ul>
+<p><a href="<?php echo esc_url($settings_url); ?>" class="button">Открыть настройки →</a></p>