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/GroupClass/GroupClassControllerTest.php

@@ -65,6 +65,7 @@ class GroupClassControllerTest extends TestCase
             static fn (string $format, string $date) => date($format, (int) strtotime($date))
         );
         Functions\when('wp_nonce_field')->justReturn('');
+        Functions\when('current_time')->justReturn('2026-01-01');
 
         $_GET = [];
     }
@@ -183,6 +184,49 @@ class GroupClassControllerTest extends TestCase
         self::assertStringContainsString('Invite by email', $html);
     }
 
+    public function testClassDetailOffersDirectAddForPublicClassWithoutInviteControls(): void
+    {
+        Functions\when('get_userdata')->justReturn($this->userNamed('Ada Lovelace'));
+        $_GET = ['class_id' => '8'];
+
+        // A plain public group class — the instructor can still add students
+        // directly (a late enrolment), but the invite-only controls are absent.
+        $offering = $this->offering(8, 'Choir', 10);
+
+        $this->offerings->shouldReceive('findAll')->once()->andReturn([$offering]);
+        $this->enrollments->shouldReceive('findByInstructor')->once()->with(3)->andReturn([]);
+
+        $html = $this->renderInstructor();
+
+        self::assertStringContainsString('Add students directly', $html);
+        self::assertStringContainsString('add_direct', $html);
+        self::assertStringNotContainsString('Invite by email', $html);
+        self::assertStringNotContainsString('Make available to students', $html);
+    }
+
+    public function testClassDetailFlagsLateEnrolmentPastTheDeadline(): void
+    {
+        Functions\when('get_userdata')->justReturn($this->userNamed('Ada Lovelace'));
+        // current_time is stubbed to 2026-01-01, which is past this class's deadline.
+        $_GET = ['class_id' => '8'];
+
+        $offering = new Offering(
+            instructorId: 3,
+            kind:         Offering::KIND_GROUP_CLASS,
+            title:        'Choir',
+            termStart:    '2025-09-08',
+            id:           8,
+        );
+
+        $this->offerings->shouldReceive('findAll')->once()->andReturn([$offering]);
+        $this->enrollments->shouldReceive('findByInstructor')->once()->with(3)->andReturn([]);
+
+        $html = $this->renderInstructor();
+
+        self::assertStringContainsString('late enrolments', $html);
+        self::assertStringContainsString('Add students directly', $html);
+    }
+
     public function testClassDetailEnrolmentCountExcludesCancelledButRosterKeepsThem(): void
     {
         Functions\when('get_userdata')->justReturn($this->userNamed('Grace Hopper'));