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/AdminMenu.php

@@ -10,17 +10,21 @@ use Unsupervised\Schedular\Booking\BookingRepository;
 use Unsupervised\Schedular\Booking\LessonController;
 use Unsupervised\Schedular\Offering\OfferingController;
 use Unsupervised\Schedular\Offering\OfferingRepository;
+use Unsupervised\Schedular\Registration\QuestionController;
+use Unsupervised\Schedular\Registration\QuestionRepository;
 
 class AdminMenu {
 
 	private AvailabilityController $availabilityController;
 	private LessonController $lessonController;
 	private OfferingController $offeringController;
+	private QuestionController $questionController;
 
-	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings, OfferingRepository $offerings ) {
+	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings, OfferingRepository $offerings, QuestionRepository $questions ) {
 		$this->availabilityController = new AvailabilityController( $availability );
 		$this->lessonController       = new LessonController( $bookings );
 		$this->offeringController     = new OfferingController( $offerings );
+		$this->questionController     = new QuestionController( $questions, $offerings );
 	}
 
 	public function register(): void {
@@ -61,6 +65,16 @@ class AdminMenu {
 			33
 		);
 
+		// Studio admin / instructor: manage per-offering intake questions.
+		add_submenu_page(
+			'us-offerings',
+			__( 'Questions', 'unsupervised-schedular' ),
+			__( 'Questions', 'unsupervised-schedular' ),
+			RoleManager::CAP_MANAGE_QUESTIONS,
+			'us-questions',
+			[ $this->questionController, 'renderPage' ]
+		);
+
 		// Instructor: view their upcoming lessons.
 		add_menu_page(
 			__( 'My Lessons', 'unsupervised-schedular' ),