Notify instructors on new bookings and enrolments

Add an opt-in, per-instructor email notice sent when someone books one of
their lessons or enrols in one of their group classes. Off by default and
set from My Availability → Notifications; covers both the student/guardian
REST flows and the studio's wp-admin "book/add for a student" forms.

The opt-in check lives in InstructorNotificationMailer so no booking path
can drift on who is mailed; lessons fire from LessonBooker::settle (the one
step both booking paths reach), enrolments from EnrollmentEndpoint::enroll
and GroupClassController::addDirect. The notice is a courtesy and never
fails a booking or enrolment that otherwise succeeded.

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

tests/Unit/Availability/AvailabilityControllerTest.php

@@ -5,6 +5,7 @@ namespace Unsupervised\Schedular\Tests\Unit\Availability;
 
 use Brain\Monkey\Functions;
 use Mockery;
+use Unsupervised\Schedular\Auth\InstructorNotificationPref;
 use Unsupervised\Schedular\Availability\AvailabilityController;
 use Unsupervised\Schedular\Availability\AvailabilityRepository;
 use Unsupervised\Schedular\Availability\AvailabilitySlot;
@@ -16,6 +17,7 @@ class AvailabilityControllerTest extends TestCase
 {
     private AvailabilityRepository&Mockery\MockInterface $repository;
     private OfferingRepository&Mockery\MockInterface $offerings;
+    private InstructorNotificationPref&Mockery\MockInterface $notifyPref;
     private AvailabilityController $controller;
 
     protected function setUp(): void
@@ -24,7 +26,12 @@ class AvailabilityControllerTest extends TestCase
 
         $this->repository = Mockery::mock(AvailabilityRepository::class);
         $this->offerings  = Mockery::mock(OfferingRepository::class);
-        $this->controller = new AvailabilityController($this->repository, $this->offerings, new WindowValidator($this->offerings));
+        // The notification preference is exercised in its own tests; here it simply
+        // reads off and accepts any save, so availability tests stay about slots.
+        $this->notifyPref = Mockery::mock(InstructorNotificationPref::class);
+        $this->notifyPref->shouldReceive('wants')->andReturn(false)->byDefault();
+        $this->notifyPref->shouldReceive('set')->byDefault();
+        $this->controller = new AvailabilityController($this->repository, $this->offerings, new WindowValidator($this->offerings), $this->notifyPref);
 
         $_POST = [];
         $_GET  = [];
@@ -286,6 +293,29 @@ class AvailabilityControllerTest extends TestCase
         self::assertStringContainsString('1 slot could not be deleted', $html);
     }
 
+    public function testTickingTheNotificationBoxSavesAnOptIn(): void
+    {
+        $_POST = ['usc_action' => 'save_notify', 'notify_on_booking' => '1'];
+
+        $this->notifyPref->shouldReceive('set')->once()->with(3, true);
+        $this->repository->shouldReceive('findByInstructor')->once()->with(3)->andReturn([]);
+
+        $html = $this->render();
+
+        self::assertStringContainsString('notice-success', $html);
+        self::assertStringContainsString('Notification preference saved.', $html);
+    }
+
+    public function testLeavingTheNotificationBoxUntickedSavesAnOptOut(): void
+    {
+        $_POST = ['usc_action' => 'save_notify'];
+
+        $this->notifyPref->shouldReceive('set')->once()->with(3, false);
+        $this->repository->shouldReceive('findByInstructor')->once()->with(3)->andReturn([]);
+
+        $this->render();
+    }
+
     private function render(): string
     {
         ob_start();