feat: fase 2 backend — crowd types, persons, sections, shifts, invite flow

- Crowd Types + Persons CRUD (73 tests)
- Festival Sections + Time Slots + Shifts CRUD met assign/claim flow (84 tests)
- Invite Flow + Member Management met InvitationService (109 tests)
- Schema v1.6 migraties volledig uitgevoerd
- DevSeeder bijgewerkt met crowd types voor testorganisatie

api/app/Http/Resources/Api/V1/ShiftAssignmentResource.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Resources\Api\V1;
+
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+final class ShiftAssignmentResource extends JsonResource
+{
+    public function toArray(Request $request): array
+    {
+        return [
+            'id' => $this->id,
+            'shift_id' => $this->shift_id,
+            'person_id' => $this->person_id,
+            'status' => $this->status,
+            'auto_approved' => $this->auto_approved,
+            'assigned_at' => $this->assigned_at?->toIso8601String(),
+            'approved_at' => $this->approved_at?->toIso8601String(),
+        ];
+    }
+}