Add invite-only group classes

Group classes can now be marked invite-only (us_offerings.access_mode).
Invite-only classes are hidden from the public catalog and reachable only
when the instructor lets someone in via one of three paths, managed from
My Lessons -> My Group Classes:

- Add students directly: enrols them now with a pending payment.
- Make available: grants registered students access to self-enrol through
  the normal paid flow (multi-select, emailed a notice).
- Invite by email: tokenised registration invite tied to the class for a
  non-account address; after they register the class becomes enrollable.
  Reuses an existing pending invite instead of sending a second link.

New us_group_access table records grants; GET /offerings merges granted
invite-only classes for the caller; enrolment requires a grant
(403 invite_required) and flips it to enrolled on success.

composer test (487), composer lint, composer cs all pass.

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

tests/Unit/Offering/OfferingTest.php

@@ -132,11 +132,53 @@ class OfferingTest extends TestCase
         $offering = new Offering(1, Offering::KIND_PRIVATE_LESSON, 'Lesson', id: 10);
         $arr      = $offering->toArray();
 
-        foreach (['id', 'instructor_id', 'kind', 'title', 'price', 'billing_mode', 'is_active'] as $key) {
+        foreach (['id', 'instructor_id', 'kind', 'title', 'price', 'billing_mode', 'access_mode', 'is_active'] as $key) {
             self::assertArrayHasKey($key, $arr);
         }
     }
 
+    public function testDefaultsToPublicAccess(): void
+    {
+        $offering = new Offering(1, Offering::KIND_GROUP_CLASS, 'Choir', id: 10);
+
+        self::assertSame(Offering::ACCESS_PUBLIC, $offering->accessMode);
+        self::assertFalse($offering->isInviteOnly());
+    }
+
+    public function testInviteOnlyAccessIsReported(): void
+    {
+        $offering = new Offering(1, Offering::KIND_GROUP_CLASS, 'Choir', accessMode: Offering::ACCESS_INVITE_ONLY, id: 10);
+
+        self::assertTrue($offering->isInviteOnly());
+        self::assertSame(Offering::ACCESS_INVITE_ONLY, $offering->toArray()['access_mode']);
+    }
+
+    public function testFromRowReadsInviteOnlyAccessMode(): void
+    {
+        $row = (object) [
+            'id'               => '7',
+            'instructor_id'    => '3',
+            'kind'             => Offering::KIND_GROUP_CLASS,
+            'title'            => 'Private Choir',
+            'description'      => null,
+            'duration_minutes' => null,
+            'price'            => '0.00',
+            'currency'         => 'CAD',
+            'billing_mode'     => Offering::BILLING_FULL_TERM,
+            'allow_weekly'     => '0',
+            'capacity'         => null,
+            'term_start'       => null,
+            'term_end'         => null,
+            'schedule_note'    => null,
+            'etransfer_email'  => null,
+            'cancellation_cutoff_hours' => null,
+            'access_mode'      => Offering::ACCESS_INVITE_ONLY,
+            'is_active'        => '1',
+        ];
+
+        self::assertTrue(Offering::fromRow($row)->isInviteOnly());
+    }
+
     public function testToArrayIncludesEtransferEmailByDefault(): void
     {
         $offering = new Offering(1, Offering::KIND_PRIVATE_LESSON, 'Lesson', etransferEmail: '[email protected]', id: 10);