feat: festival/series model with sub-events, cross-event sections, tab navigation, SectionsShiftsPanel extraction

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Http/Requests/Api/V1/ReorderFestivalSectionsRequest.php

@@ -17,9 +17,8 @@ final class ReorderFestivalSectionsRequest extends FormRequest
     public function rules(): array
     {
         return [
-            'sections' => ['required', 'array'],
-            'sections.*.id' => ['required', 'ulid'],
-            'sections.*.sort_order' => ['required', 'integer', 'min:0'],
+            'sections' => ['required', 'array', 'min:1'],
+            'sections.*' => ['required', 'ulid'],
         ];
     }
 }