Add e-transfer destination email (studio default + offering/booking overrides)

The e-transfer destination is resolved at booking time (offering override ->
studio default) and frozen onto the payment, so each record keeps where the
student was directed. It can then be corrected per booking.

- StudioSettings: us_etransfer_email option + a Default e-transfer email field
  on the Studio Settings page.
- Offering: etransfer_email column/field (instructor override) across VO, repo,
  REST endpoint, admin controller, and form.
- Payment: etransfer_email column on the payment (frozen record) +
  PaymentRepository::updateEtransferEmail; PaymentService freezes it from the
  offering override or studio default at creation; booking/enrolment pass the
  offering override.
- My Lessons: instructors edit the e-transfer email per pending lesson payment
  (ownership-checked).
- Payments queue: studio admin can correct the email at confirmation (for when
  a student sends it to the wrong place).
- Docs updated.

Tests: Payment/Offering rows + PaymentService freezing. composer test (148),
cs, and PHPStan level 6 all pass.

Refs #7

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/Unit/Payment/PaymentServiceTest.php

@@ -13,6 +13,7 @@ use Unsupervised\Schedular\Payment\Payment;
 use Unsupervised\Schedular\Payment\PaymentRepository;
 use Unsupervised\Schedular\Payment\PaymentService;
 use Unsupervised\Schedular\Payment\ReceiptMailer;
+use Unsupervised\Schedular\Payment\StudioSettings;
 use Unsupervised\Schedular\Tests\Unit\TestCase;
 
 class PaymentServiceTest extends TestCase
@@ -22,6 +23,7 @@ class PaymentServiceTest extends TestCase
     private ReceiptMailer $mailer;
     private BookingRepository $bookings;
     private EnrollmentRepository $enrollments;
+    private StudioSettings $settings;
     private PaymentService $service;
 
     protected function setUp(): void
@@ -33,13 +35,16 @@ class PaymentServiceTest extends TestCase
         $this->mailer      = Mockery::mock(ReceiptMailer::class);
         $this->bookings    = Mockery::mock(BookingRepository::class);
         $this->enrollments = Mockery::mock(EnrollmentRepository::class);
+        $this->settings    = Mockery::mock(StudioSettings::class);
+        $this->settings->shouldReceive('etransferEmail')->andReturn('');
 
         $this->service = new PaymentService(
             $this->payments,
             $this->resolver,
             $this->mailer,
             $this->bookings,
-            $this->enrollments
+            $this->enrollments,
+            $this->settings
         );
 
         Functions\when('get_userdata')->justReturn(false);
@@ -71,6 +76,21 @@ class PaymentServiceTest extends TestCase
         self::assertSame(Payment::STATUS_PENDING, $result->status);
     }
 
+    public function testOfferingEtransferEmailIsFrozenOntoPayment(): void
+    {
+        $this->resolver->shouldReceive('resolve')->with(5)->andReturn(Payment::METHOD_ETRANSFER);
+        $this->payments->shouldReceive('insert')
+            ->once()
+            ->with(Mockery::on(static fn (Payment $p): bool => $p->etransferEmail === 'pay@studio.test'))
+            ->andReturn(50);
+        $this->bookings->shouldReceive('setPaymentId')->once()->with(12, 50);
+        $this->payments->shouldReceive('findById')->with(50)->andReturn($this->payment(Payment::METHOD_ETRANSFER, Payment::STATUS_PENDING, 50));
+
+        self::assertNotNull(
+            $this->service->createForRegistration(Payment::REG_LESSON, 12, 5, 3, 35.00, 'CAD', 'pay@studio.test')
+        );
+    }
+
     public function testCompIsPaidAndConfirmsImmediately(): void
     {
         $this->resolver->shouldReceive('resolve')->with(5)->andReturn(Payment::METHOD_COMP);