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/Auth/RegistrationPageTest.php

@@ -9,6 +9,7 @@ use Unsupervised\Schedular\Auth\Invite;
 use Unsupervised\Schedular\Auth\InviteRepository;
 use Unsupervised\Schedular\Auth\RegistrationMailer;
 use Unsupervised\Schedular\Auth\RegistrationPage;
+use Unsupervised\Schedular\GroupClass\GroupAccessRepository;
 use Unsupervised\Schedular\Payment\StudioSettings;
 use Unsupervised\Schedular\Policy\AcceptanceRepository;
 use Unsupervised\Schedular\Policy\Policy;
@@ -45,11 +46,15 @@ class RegistrationPageTest extends TestCase
         $questions->shouldReceive('findByScope')->andReturn([])->byDefault();
         $answers->shouldReceive('insert')->andReturn(1)->byDefault();
 
+        $access = Mockery::mock(GroupAccessRepository::class);
+        $access->shouldReceive('linkStudentByEmail')->andReturn(true)->byDefault();
+
         $this->ctx = [
             'invites'   => $invites,
             'policies'  => $policies,
             'questions' => $questions,
             'answers'   => $answers,
+            'access'    => $access,
             'mailer'    => Mockery::mock(RegistrationMailer::class),
             'settings'  => Mockery::mock(StudioSettings::class),
         ];
@@ -63,6 +68,7 @@ class RegistrationPageTest extends TestCase
             $this->ctx['mailer'],
             $questions,
             $answers,
+            $access,
         );
 
         $_POST = [];
@@ -110,6 +116,26 @@ class RegistrationPageTest extends TestCase
         self::assertSame('invite', $this->submit($invite, false));
     }
 
+    public function testInviteAcceptanceLinksClassGrantForTheEmail(): void
+    {
+        $_POST = [ 'password' => 'password123', 'display_name' => 'Ada' ];
+
+        Functions\when('email_exists')->justReturn(false);
+        Functions\when('wp_insert_user')->justReturn(42);
+        Functions\when('is_wp_error')->justReturn(false);
+
+        $this->ctx['invites']->shouldReceive('markAccepted')->once();
+        Functions\when('wp_set_current_user')->justReturn(null);
+        Functions\when('wp_set_auth_cookie')->justReturn(null);
+
+        // A personal invite tied to a class grant links the new account to it.
+        $this->ctx['access']->shouldReceive('linkStudentByEmail')->once()->with('[email protected]', 42)->andReturn(true);
+
+        $invite = new Invite(email: '[email protected]', token: 'hash', offeringId: 8);
+
+        self::assertSame('invite', $this->submit($invite, false));
+    }
+
     public function testOpenBranchCreatesPendingWithoutLoginAndEmails(): void
     {
         $_POST = [ 'password' => 'password123', 'display_name' => 'Ada', 'email' => '[email protected]' ];