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/Organisation.php

@@ -47,4 +47,14 @@ final class Organisation extends Model
     {
         return $this->hasMany(UserInvitation::class);
     }
+
+    public function crowdTypes(): HasMany
+    {
+        return $this->hasMany(CrowdType::class);
+    }
+
+    public function companies(): HasMany
+    {
+        return $this->hasMany(Company::class);
+    }
 }