Add HST/tax support and payment reporting with HST aggregation

Studio Settings gains a default HST rate; the rate is frozen onto each
payment at booking and computed against the pre-tax subtotal, with the
total billed as subtotal + tax. The rate is overridable per booking on
My Lessons while unpaid (recomputing the tax amount), comped
registrations are never taxed, and receipts break out subtotal/HST/total.

Builds the payments report (roadmap #8) from us_payments: a monthly
per-instructor view with subtotal, HST collected, and grand-total
aggregation, plus a nonce-protected CSV export via admin-post. Studio
admins see all instructors and can filter; instructors are scoped to
their own rows. The Payment Report menu is gated on export_payments so
instructors (who lack manage_billing) can reach it.

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

tests/Unit/Payment/PaymentServiceTest.php

@@ -37,6 +37,7 @@ class PaymentServiceTest extends TestCase
         $this->enrollments = Mockery::mock(EnrollmentRepository::class);
         $this->settings    = Mockery::mock(StudioSettings::class);
         $this->settings->shouldReceive('etransferEmail')->andReturn('');
+        $this->settings->shouldReceive('hstRate')->andReturn(0.0)->byDefault();
 
         $this->service = new PaymentService(
             $this->payments,
@@ -91,6 +92,37 @@ class PaymentServiceTest extends TestCase
         );
     }
 
+    public function testHstIsComputedAndFrozenOntoPayment(): void
+    {
+        $this->settings->shouldReceive('hstRate')->andReturn(13.0);
+        $this->resolver->shouldReceive('resolve')->with(5)->andReturn(Payment::METHOD_ETRANSFER);
+        $this->payments->shouldReceive('insert')
+            ->once()
+            ->with(Mockery::on(static fn (Payment $p): bool => $p->taxRate === 13.0 && $p->taxAmount === 13.00 && $p->total() === 113.00))
+            ->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, 100.00, 'CAD'));
+    }
+
+    public function testCompIsNotTaxed(): void
+    {
+        $this->settings->shouldReceive('hstRate')->andReturn(13.0);
+        $this->resolver->shouldReceive('resolve')->with(5)->andReturn(Payment::METHOD_COMP);
+        $this->payments->shouldReceive('insert')
+            ->once()
+            ->with(Mockery::on(static fn (Payment $p): bool => $p->taxRate === 0.0 && $p->taxAmount === 0.0))
+            ->andReturn(61);
+        $this->bookings->shouldReceive('setPaymentId')->once()->with(12, 61);
+        $this->payments->shouldReceive('markPaid')->once()->with(61, 'USC-61')->andReturn(true);
+        $this->bookings->shouldReceive('updateStatus')->once()->with(12, Lesson::STATUS_CONFIRMED)->andReturn(true);
+        $this->payments->shouldReceive('findById')->with(61)->andReturn($this->payment(Payment::METHOD_COMP, Payment::STATUS_PAID, 61));
+        $this->mailer->shouldReceive('send')->andReturn(false);
+
+        self::assertNotNull($this->service->createForRegistration(Payment::REG_LESSON, 12, 5, 3, 100.00, 'CAD'));
+    }
+
     public function testCompIsPaidAndConfirmsImmediately(): void
     {
         $this->resolver->shouldReceive('resolve')->with(5)->andReturn(Payment::METHOD_COMP);