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/UserInvitation.php

@@ -48,6 +48,26 @@ final class UserInvitation extends Model
         return $this->belongsTo(Event::class);
     }
 
+    public function isExpired(): bool
+    {
+        return $this->expires_at->isPast();
+    }
+
+    public function isPending(): bool
+    {
+        return $this->status === 'pending';
+    }
+
+    public function markAsAccepted(): void
+    {
+        $this->update(['status' => 'accepted']);
+    }
+
+    public function markAsExpired(): void
+    {
+        $this->update(['status' => 'expired']);
+    }
+
     public function scopePending(Builder $query): Builder
     {
         return $query->where('status', 'pending');