Add group-class enrolment (year commitment, capacity, registration gate)

Implements #4: students enrol in a group_class offering via the same
registration gate as private lessons (intake questions + booking-scoped
policy acceptance). Enrolment is capacity-enforced and prevents duplicates.

- Schema: us_group_enrollments table.
- Enrollment value object + EnrollmentRepository (countActiveForOffering,
  hasActiveEnrollment, per-student/instructor/all-active queries, status).
- EnrollmentEndpoint: GET /enrollments (scoped) and POST /enrollments
  (validates group_class, capacity, no-duplicate; reuses RegistrationGate;
  records answers/acceptances type enrollment).
- GroupClassController + admin page (view_all_lessons): all active enrolments.
- Front-end: [us_group_classes] shortcode (GroupClassPage) + group-classes.js
  enrol flow (list classes -> questions + policies -> POST /enrollments).
- Wiring in Plugin, RestRegistrar, AdminMenu, ShortcodeRegistrar.

Payment is the deferred seam (#7): enrolment lands active, payment_id null.
JS left untested for parity with the repo's no-build vanilla-JS posture.

Tests: tests/Unit/GroupClass/ (Enrollment, EnrollmentRepository).
composer test (121), cs, and PHPStan level 6 all pass.

Refs #4

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

src/ShortcodeRegistrar.php

@@ -7,6 +7,7 @@ use Unsupervised\Schedular\Auth\InviteRepository;
 use Unsupervised\Schedular\Auth\LoginPage;
 use Unsupervised\Schedular\Auth\RegistrationPage;
 use Unsupervised\Schedular\Booking\BookingPage;
+use Unsupervised\Schedular\GroupClass\GroupClassPage;
 use Unsupervised\Schedular\Policy\AcceptanceRepository;
 use Unsupervised\Schedular\Policy\PolicyRepository;
 use Unsupervised\Schedular\Policy\PolicyVersionRepository;
@@ -16,6 +17,7 @@ class ShortcodeRegistrar {
 	private BookingPage $bookingPage;
 	private LoginPage $loginPage;
 	private RegistrationPage $registrationPage;
+	private GroupClassPage $groupClassPage;
 
 	public function __construct(
 		InviteRepository $invites,
@@ -26,27 +28,30 @@ class ShortcodeRegistrar {
 		$this->bookingPage      = new BookingPage();
 		$this->loginPage        = new LoginPage();
 		$this->registrationPage = new RegistrationPage( $invites, $policies, $policyVersions, $acceptances );
+		$this->groupClassPage   = new GroupClassPage();
 	}
 
 	public function register(): void {
 		add_shortcode( 'us_booking', [ $this->bookingPage, 'render' ] );
 		add_shortcode( 'us_student_login', [ $this->loginPage, 'render' ] );
 		add_shortcode( 'us_student_register', [ $this->registrationPage, 'render' ] );
+		add_shortcode( 'us_group_classes', [ $this->groupClassPage, 'render' ] );
 		add_action( 'template_redirect', [ $this->registrationPage, 'maybeRedirectToRegistrationPage' ] );
 		add_action( 'wp_enqueue_scripts', [ $this, 'enqueueAssets' ] );
 	}
 
 	public function enqueueAssets(): void {
 		wp_register_style( 'us-scheduler', USC_PLUGIN_URL . 'assets/css/frontend.css', [], USC_VERSION );
-		wp_register_script( 'us-scheduler', USC_PLUGIN_URL . 'assets/js/booking.js', [], USC_VERSION, true );
 
-		wp_localize_script(
-			'us-scheduler',
-			'usScheduler',
-			[
-				'restUrl' => rest_url( 'us-scheduler/v1/' ),
-				'nonce'   => wp_create_nonce( 'wp_rest' ),
-			]
-		);
+		$data = [
+			'restUrl' => rest_url( 'us-scheduler/v1/' ),
+			'nonce'   => wp_create_nonce( 'wp_rest' ),
+		];
+
+		wp_register_script( 'us-scheduler', USC_PLUGIN_URL . 'assets/js/booking.js', [], USC_VERSION, true );
+		wp_localize_script( 'us-scheduler', 'usScheduler', $data );
+
+		wp_register_script( 'us-scheduler-group', USC_PLUGIN_URL . 'assets/js/group-classes.js', [], USC_VERSION, true );
+		wp_localize_script( 'us-scheduler-group', 'usScheduler', $data );
 	}
 }