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/Payment/PaymentRepository.php

@@ -25,6 +25,9 @@ class PaymentRepository {
 				'status'                   => $payment->status,
 				'tax_rate'                 => $payment->taxRate,
 				'tax_amount'               => $payment->taxAmount,
+				'due_date'                 => $payment->dueDate,
+				'period_key'               => $payment->periodKey,
+				'notice_batch'             => $payment->noticeBatch,
 				'etransfer_email'          => $payment->etransferEmail,
 				'stripe_payment_intent_id' => $payment->stripePaymentIntentId,
 				'receipt_number'           => $payment->receiptNumber,
@@ -32,7 +35,7 @@ class PaymentRepository {
 				'paid_at'                  => $payment->paidAt,
 				'created_at'               => current_time( 'mysql' ),
 			],
-			[ '%d', '%d', '%s', '%d', '%f', '%s', '%s', '%s', '%f', '%f', '%s', '%s', '%s', '%s', '%s', '%s' ]
+			[ '%d', '%d', '%s', '%d', '%f', '%s', '%s', '%s', '%f', '%f', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s' ]
 		);
 
 		return $this->db->insert_id;
@@ -119,6 +122,51 @@ class PaymentRepository {
 		return $row ? Payment::fromRow( $row ) : null;
 	}
 
+	/**
+	 * Tag a set of payments with a shared notice-batch reference — the payments the
+	 * daily scan emailed a student together, so the admin can see which pending
+	 * payments a single lump-sum e-transfer covers. No-op for an empty id list.
+	 *
+	 * @param list<int> $ids
+	 */
+	public function assignNoticeBatch( array $ids, string $batch ): void {
+		if ( [] === $ids ) {
+			return;
+		}
+
+		$placeholders = implode( ', ', array_fill( 0, count( $ids ), '%d' ) );
+		$sql          = $this->db->prepare(
+			"UPDATE %i SET notice_batch = %s WHERE id IN ( {$placeholders} )",
+			$this->table,
+			$batch,
+			...$ids
+		);
+
+		if ( null !== $sql ) {
+			$this->db->query( $sql );
+		}
+	}
+
+	/**
+	 * Whether a scheduled payment already exists for a registration and billing
+	 * period. The daily billing scan uses this to avoid double-billing an
+	 * enrolment for the same session (weekly) or month (monthly). A voided
+	 * (`failed`) row still counts so a cancelled charge is not silently re-created.
+	 */
+	public function existsForPeriod( string $registrationType, int $registrationId, string $periodKey ): bool {
+		$found = $this->db->get_var(
+			$this->db->prepare(
+				'SELECT id FROM %i WHERE registration_type = %s AND registration_id = %d AND period_key = %s LIMIT 1',
+				$this->table,
+				$registrationType,
+				$registrationId,
+				$periodKey
+			)
+		);
+
+		return null !== $found;
+	}
+
 	public function findByRegistration( string $registrationType, int $registrationId ): ?Payment {
 		$row = $this->db->get_row(
 			$this->db->prepare(