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/Models/ShiftAssignment.php

@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Concerns\HasUlids;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\SoftDeletes;
+
+final class ShiftAssignment extends Model
+{
+    use HasFactory;
+    use HasUlids;
+    use SoftDeletes;
+
+    protected $fillable = [
+        'shift_id',
+        'person_id',
+        'time_slot_id',
+        'status',
+        'auto_approved',
+        'assigned_by',
+        'assigned_at',
+        'approved_by',
+        'approved_at',
+        'rejection_reason',
+        'hours_expected',
+        'hours_completed',
+        'checked_in_at',
+        'checked_out_at',
+    ];
+
+    protected function casts(): array
+    {
+        return [
+            'auto_approved' => 'boolean',
+            'assigned_at' => 'datetime',
+            'approved_at' => 'datetime',
+            'checked_in_at' => 'datetime',
+            'checked_out_at' => 'datetime',
+        ];
+    }
+
+    public function shift(): BelongsTo
+    {
+        return $this->belongsTo(Shift::class);
+    }
+
+    public function person(): BelongsTo
+    {
+        return $this->belongsTo(Person::class);
+    }
+
+    public function timeSlot(): BelongsTo
+    {
+        return $this->belongsTo(TimeSlot::class);
+    }
+}