Add Registration Questions domain (per-offering intake forms)

Implements #5: studio admin / instructors author intake questions scoped
per offering; answers are stored against a lesson or group enrolment via a
polymorphic registration reference.

- src/Registration/: Question + Answer value objects, QuestionRepository
  and AnswerRepository, QuestionEndpoint (REST), QuestionController +
  templates/admin/questions.php (Offerings -> Questions submenu)
- us_questions and us_question_answers tables in Schema.php
- REST: public GET /offerings/{id}/questions; POST/PATCH/DELETE /questions
  gated by manage_questions + offering ownership (owner or studio admin)
- Field types text/textarea/select/checkbox; select options stored as JSON
- Wiring in Plugin, RestRegistrar, AdminMenu

AnswerRepository is built now and consumed by the booking/enrolment flow
in #3/#4.

Tests: tests/Unit/Registration/ (19 tests). composer test (63 total), cs,
and PHPStan level 6 all pass.

Refs #5

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RestRegistrar.php

@@ -9,6 +9,8 @@ use Unsupervised\Schedular\Booking\BookingEndpoint;
 use Unsupervised\Schedular\Booking\BookingRepository;
 use Unsupervised\Schedular\Offering\OfferingEndpoint;
 use Unsupervised\Schedular\Offering\OfferingRepository;
+use Unsupervised\Schedular\Registration\QuestionEndpoint;
+use Unsupervised\Schedular\Registration\QuestionRepository;
 
 class RestRegistrar {
 
@@ -17,11 +19,13 @@ class RestRegistrar {
 	private AvailabilityEndpoint $availabilityEndpoint;
 	private BookingEndpoint $bookingEndpoint;
 	private OfferingEndpoint $offeringEndpoint;
+	private QuestionEndpoint $questionEndpoint;
 
-	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings, OfferingRepository $offerings ) {
+	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings, OfferingRepository $offerings, QuestionRepository $questions ) {
 		$this->availabilityEndpoint = new AvailabilityEndpoint( $availability );
 		$this->bookingEndpoint      = new BookingEndpoint( $availability, $bookings );
 		$this->offeringEndpoint     = new OfferingEndpoint( $offerings );
+		$this->questionEndpoint     = new QuestionEndpoint( $questions, $offerings );
 	}
 
 	public function register(): void {
@@ -32,5 +36,6 @@ class RestRegistrar {
 		$this->availabilityEndpoint->registerRoutes( self::NAMESPACE );
 		$this->bookingEndpoint->registerRoutes( self::NAMESPACE );
 		$this->offeringEndpoint->registerRoutes( self::NAMESPACE );
+		$this->questionEndpoint->registerRoutes( self::NAMESPACE );
 	}
 }