Add weekly and monthly scheduled billing for offerings

Offerings can now bill weekly (a pending payment 24h before each lesson)
or monthly (one payment on the 1st for that month's lessons), alongside
one-time and full-term. Applies to both private lessons and group classes.

- Offering: new `weekly`/`monthly` billing modes + `isScheduledBilling()`
- Booking/enrolment defer payment for scheduled modes; a single lesson
  booked after its due date has passed (e.g. an add-on in an already-billed
  month) is charged at booking instead
- ScheduledBillingRunner: daily WP-Cron scan generates due payments across
  four cases (private/group × weekly/monthly), deduped via lesson.payment_id
  and payments.period_key
- PaymentDueMailer: one consolidated itemised email per student per scan
- Notice batch: payments emailed together share a reference; the admin
  Payments queue groups them with a lump-sum total for e-transfer reconciliation
- Cancellation never voids a scheduled payment (Payment::isScheduled())
- Schema: us_payments gains due_date, period_key, notice_batch; USC_VERSION 1.2.0

composer test, composer lint, composer cs all pass.

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

src/GroupClass/EnrollmentEndpoint.php

@@ -129,8 +129,11 @@ class EnrollmentEndpoint {
 			$this->access->markEnrolled( $offeringId, $studentId );
 		}
 
+		// Scheduled billing (weekly / monthly) is generated later by the daily
+		// billing scan, so nothing is charged at enrolment; the enrolment is active
+		// regardless of payment.
 		$payment = null;
-		if ( $offering->price > 0.0 ) {
+		if ( $offering->price > 0.0 && ! $offering->isScheduledBilling() ) {
 			$payment = $this->payments->createForRegistration( Payment::REG_ENROLLMENT, $id, $studentId, $offering->instructorId, $offering->price, $offering->currency, $offering->etransferEmail );
 		}
 

src/GroupClass/EnrollmentRepository.php

@@ -132,6 +132,39 @@ class EnrollmentRepository {
 		return array_map( Enrollment::fromRow( ... ), $rows ?? [] );
 	}
 
+	/**
+	 * Active enrolments whose group class bills on a scheduled mode (weekly /
+	 * monthly) — the source rows for the daily billing scan. Filtered by joining
+	 * the offering so only classes actually on a scheduled plan are returned.
+	 *
+	 * @param list<string> $modes Billing modes to include (e.g. weekly, monthly).
+	 * @return list<Enrollment>
+	 */
+	public function findActiveByBillingModes( array $modes ): array {
+		if ( [] === $modes ) {
+			return [];
+		}
+
+		$offTable     = str_replace( 'us_group_enrollments', 'us_offerings', $this->table );
+		$placeholders = implode( ', ', array_fill( 0, count( $modes ), '%s' ) );
+
+		$rows = $this->db->get_results(
+			$this->db->prepare(
+				"SELECT e.* FROM %i e
+				 JOIN %i o ON o.id = e.offering_id
+				 WHERE e.status = %s
+				   AND o.billing_mode IN ( {$placeholders} )
+				 ORDER BY e.student_id ASC, e.offering_id ASC",
+				$this->table,
+				$offTable,
+				Enrollment::STATUS_ACTIVE,
+				...$modes
+			)
+		);
+
+		return array_map( Enrollment::fromRow( ... ), $rows ?? [] );
+	}
+
 	public function setPaymentId( int $id, int $paymentId ): bool {
 		return false !== $this->db->update(
 			$this->table,