Add group-class enrolment deadline with instructor late-enrolment override

Group classes gain an instructor-set enrolment deadline (new
us_offerings.enrollment_deadline column) that defaults to the first day of
the class (term_start). Past the deadline students can no longer self-enrol:
the enrolment endpoint rejects it (403 enrollment_closed) and the front-end
class list shows "Enrolment has closed." in place of the Enrol button.

Instructors keep a manual path: the "Add students directly" control on each
class's details page now renders for public classes too (not just
invite-only) and deliberately bypasses the deadline and capacity, so a
student can be added as a late enrolment after the class has closed. Past
the deadline the details page labels these as late enrolments.

Bumps USC_VERSION to 1.1.3 for the schema change.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

tests/Unit/Offering/OfferingControllerTest.php

@@ -102,6 +102,43 @@ class OfferingControllerTest extends TestCase
         self::assertStringContainsString('2 open booking slots were removed', $html);
     }
 
+    public function testAddGroupClassStoresEnrollmentDeadline(): void
+    {
+        $_POST = [
+            'usc_action'          => 'add',
+            'title'               => 'Ballet Beginners',
+            'kind'                => Offering::KIND_GROUP_CLASS,
+            'term_start'          => '2026-09-08',
+            'enrollment_deadline' => '2026-08-31',
+        ];
+
+        $this->repository->shouldReceive('insert')->once()->with(Mockery::on(
+            static fn (Offering $o) => '2026-08-31' === $o->enrollmentDeadline
+        ))->andReturn(1);
+        $this->repository->shouldReceive('findAll')->andReturn([]);
+        $this->reconciler->shouldReceive('reconcile')->once()->andReturn(['removed' => 0, 'conflicts' => []]);
+
+        $this->render();
+    }
+
+    public function testBlankEnrollmentDeadlineLeavesItNullToDefaultToFirstClass(): void
+    {
+        $_POST = [
+            'usc_action' => 'add',
+            'title'      => 'Choir',
+            'kind'       => Offering::KIND_GROUP_CLASS,
+            'term_start' => '2026-09-08',
+        ];
+
+        $this->repository->shouldReceive('insert')->once()->with(Mockery::on(
+            static fn (Offering $o) => null === $o->enrollmentDeadline
+        ))->andReturn(1);
+        $this->repository->shouldReceive('findAll')->andReturn([]);
+        $this->reconciler->shouldReceive('reconcile')->once()->andReturn(['removed' => 0, 'conflicts' => []]);
+
+        $this->render();
+    }
+
     public function testGarbageClassTimeIsRejected(): void
     {
         $_POST = [