feat(admin): always-on dashboard widget + default retro days = 0

- Dashboard widget is now registered unconditionally. Header + content
  adapt: shows '⚠️ ошибки доставки' only when failed > 0, otherwise
  plain title with queue state (pending / sent-24h / failed).
  Pilot feedback: the conditional widget felt like the plugin was
  missing — users expect a persistent status readout.
- Retro default window changed from 7 days to 0 (no limit). Most
  pilot uses were 'dump everything since install', so 0 is the more
  useful default. User can still narrow to N days in the form.
- Spec §10 + §14 updated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

admin/class-dashboard-widget.php

@@ -7,15 +7,18 @@ final class Dashboard_Widget
 {
     public function register(): void
     {
-        add_action('wp_dashboard_setup', [$this, 'maybe_register_widget']);
+        add_action('wp_dashboard_setup', [$this, 'register_widget']);
     }
 
-    public function maybe_register_widget(): void
+    public function register_widget(): void
     {
-        if (Queue::count_failed() === 0) return;
+        $failed_count = Queue::count_failed();
+        $title = $failed_count > 0
+            ? '⚠️ CF7 Spam → Telegram: ошибки доставки'
+            : 'CF7 Spam → Telegram';
         wp_add_dashboard_widget(
-            'cf7stg_dashboard_errors',
-            '⚠️ CF7 Spam → Telegram: ошибки доставки',
+            'cf7stg_dashboard_status',
+            $title,
             [$this, 'render']
         );
     }
@@ -23,7 +26,10 @@ final class Dashboard_Widget
     public function render(): void
     {
         $failed = Queue::list_failed(10);
-        $count = Queue::count_failed();
+        $failed_count = Queue::count_failed();
+        $pending = Queue::count_by_status(Queue::STATUS_PENDING);
+        $sent_24h = Queue::count_sent_last_24h();
+        $configured = Settings::is_configured();
         $settings_url = admin_url('options-general.php?page=cf7stg-settings');
         include CF7STG_PLUGIN_DIR . 'admin/views/dashboard-widget.php';
     }