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/Booking/BookingEndpoint.php

@@ -259,7 +259,16 @@ class BookingEndpoint {
 		$payment = null;
 		$status  = Lesson::STATUS_PENDING;
 
-		if ( $offering->price > 0.0 ) {
+		// Scheduled billing (weekly / monthly) normally defers payment to the daily
+		// scan, but a single lesson booked once its scheduled due date has already
+		// passed — e.g. an extra lesson added to a month that was already billed — is
+		// charged at booking instead, so it is never missed or billed late.
+		$chargeAtBooking = $offering->price > 0.0 && (
+			! $offering->isScheduledBilling()
+			|| ( 1 === count( $ids ) && $this->scheduledDueHasPassed( $offering, $slot->startDt ) )
+		);
+
+		if ( $chargeAtBooking ) {
 			// A full-term price already covers the whole reservation; a per-lesson
 			// (one_time) price is owed once per occurrence actually claimed, so a
 			// weekly reservation cannot hold a term while paying for one week.
@@ -273,8 +282,10 @@ class BookingEndpoint {
 				$status = Lesson::STATUS_CONFIRMED;
 			}
 		} else {
-			// Free offering: there is no payment step that would confirm these
-			// lessons later, so they are confirmed at booking time.
+			// Either a free offering, or scheduled billing (weekly / monthly) whose
+			// payment is deferred to the daily billing scan. Either way there is no
+			// payment step now to confirm the lessons, so the reserved slots are
+			// confirmed at booking time; the billing scan bills them when they come due.
 			foreach ( $ids as $lessonId ) {
 				$this->bookings->updateStatus( $lessonId, Lesson::STATUS_CONFIRMED );
 			}
@@ -306,6 +317,23 @@ class BookingEndpoint {
 		return $out;
 	}
 
+	/**
+	 * Whether a scheduled-billing offering's due date for a given session has
+	 * already passed at booking time. Weekly bills 24 hours before the lesson;
+	 * monthly bills on the 1st, so its due moment has passed once "now" is in the
+	 * lesson's month or later. Only meaningful for weekly / monthly offerings.
+	 */
+	private function scheduledDueHasPassed( Offering $offering, string $slotStart ): bool {
+		$now   = new \DateTimeImmutable( Val::string( current_time( 'mysql' ) ) );
+		$start = new \DateTimeImmutable( $slotStart );
+
+		if ( Offering::BILLING_MONTHLY === $offering->billingMode ) {
+			return $now->format( 'Y-m-d' ) >= $start->format( 'Y-m-01' );
+		}
+
+		return $now >= $start->modify( '-1 day' );
+	}
+
 	private function clientIp(): ?string {
 		// phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized, WordPress.Security.ValidatedSanitizedInput.MissingUnslash -- IP stored verbatim for audit.
 		$ip = sanitize_text_field( Val::string( wp_unslash( $_SERVER['REMOTE_ADDR'] ?? '' ) ) );