Feature-Toggles, Administration, wiederkehrende Events und Event-Serien

- Administration & Rollenmanagement: Neuer Admin-Bereich mit Feature-Toggles
  und Sichtbarkeitseinstellungen pro Rolle (11 Toggles, 24 Visibility-Settings)
- AdministrationController mit eigenem Settings-Tab, aus SettingsController extrahiert
- Feature-Toggle-Guards in Controllers (Invitation, File, ListGenerator, Comment)
  und Views (events/show, events/edit, events/create)
- Setting::isFeatureEnabled() und isFeatureVisibleFor() Hilfsmethoden
- Wiederkehrende Trainings: Täglich/Wöchentlich/2-Wöchentlich mit Ende per
  Datum oder Anzahl (max. 52), Vorschau im Formular
- Event-Serien: Verknüpfung über event_series_id (UUID), Modal-Dialog beim
  Speichern und Löschen mit Optionen "nur dieses" / "alle folgenden"
- Löschen-Button direkt in der Event-Bearbeitung mit Serien-Dialog
- DemoDataSeeder: 4 Trainings als Serie mit gemeinsamer event_series_id
- Übersetzungen in allen 6 Sprachen (de, en, pl, ru, ar, tr)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lang/en/admin.php

@@ -626,4 +626,57 @@ return [
 
     // Visibility
     'visibility_feature_finances' => 'Finances',
+
+    // Administration
+    'nav_administration' => 'Administration',
+    'admin_title' => 'Administration',
+    'admin_tab_features' => 'Role Management',
+    'admin_tab_mail' => 'Email',
+    'admin_tab_license' => 'License & Support',
+    'admin_tab_maintenance' => 'Maintenance',
+    'admin_tab_activity' => 'Activity Log',
+    'features_description' => 'Enable or disable features globally and control visibility per role. Base features (Events, Teams, Players, Users) are always active.',
+    'feature_enabled' => 'Enabled',
+    'feature_disabled' => 'Disabled',
+    'feature_statistics' => 'Statistics',
+    'feature_finances' => 'Finances',
+    'feature_catering' => 'Catering',
+    'feature_timekeepers' => 'Timekeepers',
+    'feature_carpools' => 'Carpools',
+    'feature_comments' => 'Comments',
+    'feature_files' => 'Files',
+    'feature_faqs' => 'FAQs',
+    'feature_list_generator' => 'List Generator',
+    'feature_invitations' => 'Invitations',
+    'feature_player_stats' => 'Player Statistics',
+    'features_saved' => 'Role management saved.',
+    'activity_recent' => 'Recent Activities',
+
+    // Recurrence
+    'recurrence' => 'Recurrence',
+    'recurrence_none' => 'No recurrence',
+    'recurrence_daily' => 'Daily',
+    'recurrence_weekly' => 'Weekly',
+    'recurrence_biweekly' => 'Every 2 weeks',
+    'recurrence_end_type' => 'End of recurrence',
+    'recurrence_end_date' => 'Until date',
+    'recurrence_end_count' => 'Number of repetitions',
+    'recurrence_count_label' => 'Count (excluding first event)',
+    'recurrence_preview' => ':count additional events will be created',
+    'recurrence_max_warning' => 'Maximum :max events possible',
+    'recurrence_created' => ':count training events created.',
+
+    // Event Series
+    'save_following' => 'Update all following',
+    'series_hint' => 'This event is part of a series. There are :count more upcoming events.',
+    'save_series_title' => 'Save changes',
+    'save_series_description' => 'This event is part of a series with :count more upcoming events. Should the changes also be applied to the following events?',
+    'save_only_this' => 'Save only this event',
+    'save_this_and_following' => 'Update this and all following events',
+    'delete_series_title' => 'Delete event series',
+    'delete_series_description' => 'This event belongs to a recurring series. What would you like to delete?',
+    'delete_only_this' => 'Delete only this event',
+    'delete_this_and_following' => 'Delete this and all following events',
+    'series_events_deleted' => ':count events deleted.',
+    'series_events_updated' => 'This event and :count following events updated.',
 ];