feat: proper determination of agency initiated bookings

For booking that are agency initiated (groups) different rules apply
concerning mutability and requirement of personal data and whether the
first participant is the applicant or not. This commit adds logic to
evaluate the agency id assigned to the booking data to decide.

src/Form/Model/BookingDto.php

@@ -7,6 +7,7 @@ namespace App\Form\Model;
 use App\BusProNet\Constants;
 use App\BusProNet\Model\Booking;
 use App\BusProNet\Model\Travel;
+use App\BusProNet\XmlLoader\AgencyLoader;
 use App\Validator\Constraints as AppAssert;
 use Symfony\Component\Validator\Constraints as Assert;
 use Symfony\Component\Validator\Context\ExecutionContextInterface;
@@ -49,6 +50,8 @@ class BookingDto
 
     public ?int $agencyId = null;
 
+    public ?string $agencyCode = null;
+
     /**
      * Booking status code for API submission.
      * Values: 'F' (Final/Frei), 'A' (Anfrage/Inquiry).
@@ -310,4 +313,16 @@ class BookingDto
 
         return $oldSnapshot !== $newSnapshot;
     }
+
+    /**
+     * Determines if this booking is initiated by the internal agency.
+     *
+     * Internal agency bookings have a different relationship between applicant
+     * and first participant: the applicant is a staff member, not the first
+     * participant. This affects personal data editability rules.
+     */
+    public function isInternalAgencyBooking(): bool
+    {
+        return AgencyLoader::INTERNAL_AGENCY_CODE === $this->agencyCode;
+    }
 }