Add group-class enrolment deadline with instructor late-enrolment override

Group classes gain an instructor-set enrolment deadline (new
us_offerings.enrollment_deadline column) that defaults to the first day of
the class (term_start). Past the deadline students can no longer self-enrol:
the enrolment endpoint rejects it (403 enrollment_closed) and the front-end
class list shows "Enrolment has closed." in place of the Enrol button.

Instructors keep a manual path: the "Add students directly" control on each
class's details page now renders for public classes too (not just
invite-only) and deliberately bypasses the deadline and capacity, so a
student can be added as a late enrolment after the class has closed. Past
the deadline the details page labels these as late enrolments.

Bumps USC_VERSION to 1.1.3 for the schema change.

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

src/Offering/Offering.php

@@ -54,6 +54,7 @@ class Offering {
 		public readonly ?string $termStart = null,
 		public readonly ?string $termEnd = null,
 		public readonly ?string $classTime = null,
+		public readonly ?string $enrollmentDeadline = null,
 		public readonly ?string $scheduleNote = null,
 		public readonly ?string $etransferEmail = null,
 		public readonly ?int $cancellationCutoffHours = null,
@@ -70,6 +71,27 @@ class Offering {
 		return self::ACCESS_INVITE_ONLY === $this->accessMode;
 	}
 
+	/**
+	 * The last day on which a student may enrol in this group class. Defaults to
+	 * the first day of the class (`term_start`) when the instructor has not set an
+	 * explicit deadline; null only when the class has no dates at all.
+	 */
+	public function effectiveEnrollmentDeadline(): ?string {
+		return $this->enrollmentDeadline ?? $this->termStart;
+	}
+
+	/**
+	 * Whether enrolment is still open on `$today` (a `Y-m-d` date). Enrolment stays
+	 * open through the end of the deadline day, so the first class is still
+	 * enrollable under the default deadline. A class with no deadline at all (no
+	 * dates configured) is always open.
+	 */
+	public function isEnrollmentOpen( string $today ): bool {
+		$deadline = $this->effectiveEnrollmentDeadline();
+
+		return null === $deadline || $today <= $deadline;
+	}
+
 	/**
 	 * Normalise a submitted term date to canonical `Y-m-d`, or null when it is
 	 * not a real calendar date. Round-trips through DateTimeImmutable so
@@ -169,6 +191,7 @@ class Offering {
 			termStart:       Val::stringOrNull( $row->term_start ),
 			termEnd:         Val::stringOrNull( $row->term_end ),
 			classTime:       Val::stringOrNull( $row->class_time ?? null ),
+			enrollmentDeadline: Val::stringOrNull( $row->enrollment_deadline ?? null ),
 			scheduleNote:    Val::stringOrNull( $row->schedule_note ),
 			etransferEmail:  Val::stringOrNull( $row->etransfer_email ),
 			cancellationCutoffHours: Val::intOrNull( $row->cancellation_cutoff_hours ),
@@ -203,6 +226,7 @@ class Offering {
 			'term_start'                => $this->termStart,
 			'term_end'                  => $this->termEnd,
 			'class_time'                => $this->classTime,
+			'enrollment_deadline'       => $this->enrollmentDeadline,
 			'schedule_note'             => $this->scheduleNote,
 			'cancellation_cutoff_hours' => $this->cancellationCutoffHours,
 			'access_mode'               => $this->accessMode,