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 <[email protected]>

src/Registration/QuestionController.php

@@ -0,0 +1,111 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Registration;
+
+use Unsupervised\Schedular\Auth\RoleManager;
+use Unsupervised\Schedular\Offering\Offering;
+use Unsupervised\Schedular\Offering\OfferingRepository;
+
+class QuestionController {
+
+	public function __construct(
+		private QuestionRepository $questions,
+		private OfferingRepository $offerings,
+	) {}
+
+	public function renderPage(): void {
+		if ( ! current_user_can( RoleManager::CAP_MANAGE_QUESTIONS ) ) {
+			wp_die( esc_html__( 'You do not have permission to manage questions.', 'unsupervised-schedular' ) );
+		}
+
+		$userId    = get_current_user_id();
+		$manageAll = current_user_can( RoleManager::CAP_MANAGE_INSTRUCTORS );
+
+		// phpcs:ignore WordPress.Security.NonceVerification.Recommended -- read-only offering selector.
+		$offeringId       = absint( $_GET['offering_id'] ?? 0 );
+		$offeringList     = $manageAll ? $this->offerings->findAll() : $this->offerings->findAll( $userId );
+		$selectedOffering = $offeringId > 0 ? $this->offerings->findById( $offeringId ) : null;
+
+		if ( null !== $selectedOffering && ! $this->canManageOffering( $selectedOffering, $userId, $manageAll ) ) {
+			$selectedOffering = null;
+		}
+
+		$questions = null;
+		if ( null !== $selectedOffering ) {
+			if ( isset( $_POST['usc_action'] ) && check_admin_referer( 'usc_question_action' ) ) {
+				$this->handleFormAction( $selectedOffering );
+			}
+
+			$questions = $this->questions->findByOffering( (int) $selectedOffering->id );
+		}
+
+		include USC_PLUGIN_DIR . 'templates/admin/questions.php';
+	}
+
+	private function handleFormAction( Offering $offering ): void {
+		// Nonce is verified by the caller (renderPage) before this method runs.
+		// phpcs:disable WordPress.Security.NonceVerification.Missing
+		$action = sanitize_key( wp_unslash( $_POST['usc_action'] ?? '' ) );
+
+		if ( 'add' === $action ) {
+			$this->addQuestion( (int) $offering->id );
+		}
+
+		if ( 'delete' === $action ) {
+			$questionId = absint( $_POST['question_id'] ?? 0 );
+			if ( $questionId > 0 ) {
+				$question = $this->questions->findById( $questionId );
+				if ( $question && $question->offeringId === (int) $offering->id ) {
+					$this->questions->delete( $questionId );
+				}
+			}
+		}
+		// phpcs:enable WordPress.Security.NonceVerification.Missing
+	}
+
+	private function addQuestion( int $offeringId ): void {
+		// phpcs:disable WordPress.Security.NonceVerification.Missing
+		$label     = sanitize_text_field( wp_unslash( $_POST['label'] ?? '' ) );
+		$fieldType = sanitize_key( wp_unslash( $_POST['field_type'] ?? Question::FIELD_TEXT ) );
+
+		if ( '' === $label || ! in_array( $fieldType, Question::VALID_FIELD_TYPES, true ) ) {
+			return;
+		}
+
+		$this->questions->insert(
+			new Question(
+				offeringId: $offeringId,
+				label:      $label,
+				fieldType:  $fieldType,
+				options:    $this->parseOptions( sanitize_textarea_field( wp_unslash( $_POST['options'] ?? '' ) ) ),
+				isRequired: isset( $_POST['is_required'] ),
+				sortOrder:  absint( $_POST['sort_order'] ?? 0 ),
+			)
+		);
+		// phpcs:enable WordPress.Security.NonceVerification.Missing
+	}
+
+	private function canManageOffering( Offering $offering, int $userId, bool $manageAll ): bool {
+		return $manageAll || $offering->instructorId === $userId;
+	}
+
+	/**
+	 * Parse a newline-separated textarea into a list of option strings.
+	 *
+	 * @return list<string>|null
+	 */
+	private function parseOptions( string $raw ): ?array {
+		$lines   = preg_split( '/\r\n|\r|\n/', $raw );
+		$options = array_values(
+			array_filter(
+				array_map(
+					static fn( string $line ): string => sanitize_text_field( trim( $line ) ),
+					false === $lines ? [] : $lines
+				)
+			)
+		);
+
+		return [] === $options ? null : $options;
+	}
+}