Apply account credit on same-month rebook, surface credit on student page

A monthly/weekly lesson booked into a month whose billing date has
already passed is charged at booking time by LessonBooker::settle,
bypassing the daily scan where account credit is otherwise applied. So
rebooking a cancelled paid lesson within the same month charged the
family in full while their cancellation credit sat unused — billed twice
for the same slot.

Apply the payer's credit to that charge-at-booking payment for scheduled
offerings, mirroring the daily scan: a payment fully covered by credit
settles and confirms its lesson. Add PaymentService::findPayment so
settle can re-read the row after applyCredits writes to it.

Also surface the student's total account credit at the top of their
detail page when they hold a balance, so the studio sees it at a glance.

Co-authored-by: anthropic/claude-opus-4-8

src/Booking/LessonBooker.php

@@ -184,6 +184,7 @@ class LessonBooker {
 				? $offering->price
 				: $offering->price * count( $ids );
 
+			$payerId = $this->guardians->payerFor( $studentId );
 			$payment = $this->payments->createForRegistration(
 				Payment::REG_LESSON,
 				$anchorId,
@@ -192,9 +193,23 @@ class LessonBooker {
 				$amount,
 				$offering->currency,
 				$offering->etransferEmail,
-				payerId: $this->guardians->payerFor( $studentId )
+				payerId: $payerId
 			);
 
+			// A scheduled lesson charged at booking — the extra lesson added to (or a
+			// cancelled one rebooked within) an already-billed month — skips the daily
+			// scan, which is the only place credit is otherwise applied. Apply the
+			// payer's account credit here too, so a cancellation credit settles the
+			// rebooking instead of the family being charged twice for the same slot. A
+			// pending payment fully covered by credit is settled and its lesson
+			// confirmed; applyCredits is a no-op when the payer holds no balance. The
+			// one-time pay-now flow is left alone: its payment step already fronts the
+			// student, and credit there is a manual studio decision.
+			if ( $offering->isScheduledBilling() && null !== $payment && null !== $payment->id && Payment::STATUS_PENDING === $payment->status ) {
+				$this->payments->applyCredits( $payerId, [ $payment ] );
+				$payment = $this->payments->findPayment( (int) $payment->id ) ?? $payment;
+			}
+
 			return [
 				'status'  => null !== $payment && $payment->isPaid() ? Lesson::STATUS_CONFIRMED : Lesson::STATUS_PENDING,
 				'payment' => $payment,

src/Payment/PaymentService.php

@@ -116,6 +116,15 @@ class PaymentService {
 		return $this->payments->markNoticed( $paymentId );
 	}
 
+	/**
+	 * Re-read a payment from the ledger — the caller's way to pick up a status or
+	 * credit change {@see applyCredits} wrote straight to the row, since the
+	 * Payment object it holds is immutable. Delegates to the ledger.
+	 */
+	public function findPayment( int $paymentId ): ?Payment {
+		return $this->payments->findById( $paymentId );
+	}
+
 	/**
 	 * Studio-admin confirmation that a pending payment (e-transfer) was received.
 	 * Marks it paid, confirms the registration, and emails the receipt.