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/Question.php

@@ -0,0 +1,77 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Registration;
+
+class Question {
+
+	public const FIELD_TEXT     = 'text';
+	public const FIELD_TEXTAREA = 'textarea';
+	public const FIELD_SELECT   = 'select';
+	public const FIELD_CHECKBOX = 'checkbox';
+
+	/**
+	 * All valid field types.
+	 *
+	 * @var list<string>
+	 */
+	public const VALID_FIELD_TYPES = [
+		self::FIELD_TEXT,
+		self::FIELD_TEXTAREA,
+		self::FIELD_SELECT,
+		self::FIELD_CHECKBOX,
+	];
+
+	/**
+	 * Build an intake question value object.
+	 *
+	 * @param list<string>|null $options Choices for a `select` field.
+	 */
+	public function __construct(
+		public readonly int $offeringId,
+		public readonly string $label,
+		public readonly string $fieldType = self::FIELD_TEXT,
+		public readonly ?array $options = null,
+		public readonly bool $isRequired = false,
+		public readonly int $sortOrder = 0,
+		public readonly bool $isActive = true,
+		public readonly ?int $id = null,
+	) {}
+
+	public static function fromRow( object $row ): self {
+		$options = null;
+		if ( null !== $row->options && '' !== $row->options ) {
+			$decoded = json_decode( (string) $row->options, true );
+			$options = is_array( $decoded ) ? array_values( array_map( 'strval', $decoded ) ) : null;
+		}
+
+		return new self(
+			offeringId: (int) $row->offering_id,
+			label:      $row->label,
+			fieldType:  $row->field_type,
+			options:    $options,
+			isRequired: (bool) $row->is_required,
+			sortOrder:  (int) $row->sort_order,
+			isActive:   (bool) $row->is_active,
+			id:         (int) $row->id,
+		);
+	}
+
+	/**
+	 * Returns a plain array representation of the question.
+	 *
+	 * @return array<string, mixed>
+	 */
+	public function toArray(): array {
+		return [
+			'id'          => $this->id,
+			'offering_id' => $this->offeringId,
+			'label'       => $this->label,
+			'field_type'  => $this->fieldType,
+			'options'     => $this->options,
+			'is_required' => $this->isRequired,
+			'sort_order'  => $this->sortOrder,
+			'is_active'   => $this->isActive,
+		];
+	}
+}