Add group-class withdrawal deadline and kind-aware offering form

Group classes now carry an optional per-class withdrawal deadline. Up to
that day a student may withdraw themselves from the class; the withdrawal
frees the seat and voids any pending payment but never issues an account
credit. After the deadline self-withdrawal closes and a studio admin must
withdraw the student by hand (the admin path is never subject to the
deadline). A blank deadline keeps self-withdrawal open indefinitely.

Also make the Add/Edit Offering form show only the fields relevant to the
selected kind: group settings for group classes, weekly reservation for
private lessons. Progressive enhancement — without JS every field renders.

- New nullable us_offerings.withdrawal_deadline column; Offering model gains
  $withdrawalDeadline + isWithdrawalOpen().
- New student endpoint POST /enrollments/{id}/withdraw, gated by the deadline
  (403 withdrawal_closed), ownership-checked, idempotent.
- Front-end group-class page shows a Withdraw button while open.
- No USC_VERSION bump: 1.2.0 is unreleased and accumulates schema changes
  under its section, matching the scheduled-billing and credit features.

Tests: composer test (596), composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/GroupClass/EnrollmentEndpoint.php

@@ -59,6 +59,18 @@ class EnrollmentEndpoint {
 				],
 			]
 		);
+
+		register_rest_route(
+			$route_namespace,
+			'/enrollments/(?P<id>\d+)/withdraw',
+			[
+				[
+					'methods'             => \WP_REST_Server::CREATABLE,
+					'callback'            => [ $this, 'withdraw' ],
+					'permission_callback' => [ $this, 'isLoggedIn' ],
+				],
+			]
+		);
 	}
 
 	public function index( \WP_REST_Request $request ): \WP_REST_Response { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.Found
@@ -148,6 +160,50 @@ class EnrollmentEndpoint {
 		);
 	}
 
+	/**
+	 * Withdraw the current student from a group class they enrolled in. Allowed
+	 * only while the offering's withdrawal deadline is open (a class with no
+	 * deadline set stays open indefinitely); once it passes, the student must
+	 * contact the studio and an admin withdraws them by hand. A timely withdrawal
+	 * frees the seat and voids any still-pending payment but never issues an
+	 * account credit — that is reserved for cancelled lessons.
+	 */
+	public function withdraw( \WP_REST_Request $request ): \WP_REST_Response|\WP_Error {
+		$id         = absint( Val::int( $request->get_param( 'id' ) ) );
+		$enrollment = $this->enrollments->findById( $id );
+
+		if ( null === $enrollment ) {
+			return new \WP_Error( 'not_found', __( 'Enrolment not found.', 'unsupervised-schedular' ), [ 'status' => 404 ] );
+		}
+
+		if ( get_current_user_id() !== $enrollment->studentId ) {
+			return new \WP_Error( 'forbidden', __( 'You cannot withdraw from this class.', 'unsupervised-schedular' ), [ 'status' => 403 ] );
+		}
+
+		if ( Enrollment::STATUS_ACTIVE === $enrollment->status ) {
+			$offering = $this->offerings->findById( $enrollment->offeringId );
+
+			if ( null !== $offering && ! $offering->isWithdrawalOpen( Val::string( current_time( 'Y-m-d' ) ) ) ) {
+				return new \WP_Error(
+					'withdrawal_closed',
+					__( 'Withdrawal for this class has closed. Please contact the studio.', 'unsupervised-schedular' ),
+					[ 'status' => 403 ]
+				);
+			}
+
+			$this->enrollments->updateStatus( $id, Enrollment::STATUS_CANCELLED );
+			$this->payments->voidPending( $enrollment->paymentId );
+		}
+
+		return new \WP_REST_Response(
+			[
+				'id'     => $id,
+				'status' => Enrollment::STATUS_CANCELLED,
+			],
+			200
+		);
+	}
+
 	public function isLoggedIn(): bool {
 		return is_user_logged_in();
 	}