Add lesson booking registration flow (offering, questions, policies)

Implements #3: students register for a private lesson by picking a slot,
answering the offering's intake questions, and accepting booking-scoped
policies. Payment is a clean seam for #7 (lessons land pending; payment_id
null; instructor confirms via PATCH /bookings/{id}/status).

- Schema: us_lessons += offering_id, recurrence, series_id, payment_id.
- Lesson: new fields + recurrence constants.
- BookingRepository::insertSeries() builds a weekly series sharing a
  series_id; AvailabilityRepository::findUnbookedInGroup() reserves a group.
- RegistrationGate (src/Registration/): validate + record intake answers and
  booking-scoped policy acceptances. Reused by group enrolment (#4).
- BookingEndpoint::book(): offering_id, recurrence, answers,
  accepted_policy_version_ids; single or weekly; records answers/acceptances
  (type lesson).
- GET /policies?scope=booking filter.
- Front-end booking.js: slot -> questions + policies -> submit.
- Wiring: RegistrationGate built in Plugin, passed via RestRegistrar.
- Test-only WP_Error stub in tests/bootstrap.php for gate testing.

Refs #3

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/Unit/Registration/RegistrationGateTest.php

@@ -0,0 +1,105 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Tests\Unit\Registration;
+
+use Mockery;
+use Unsupervised\Schedular\Policy\AcceptanceRepository;
+use Unsupervised\Schedular\Policy\Policy;
+use Unsupervised\Schedular\Policy\PolicyAcceptance;
+use Unsupervised\Schedular\Policy\PolicyRepository;
+use Unsupervised\Schedular\Policy\PolicyVersion;
+use Unsupervised\Schedular\Policy\PolicyVersionRepository;
+use Unsupervised\Schedular\Registration\Answer;
+use Unsupervised\Schedular\Registration\AnswerRepository;
+use Unsupervised\Schedular\Registration\Question;
+use Unsupervised\Schedular\Registration\QuestionRepository;
+use Unsupervised\Schedular\Registration\RegistrationGate;
+use Unsupervised\Schedular\Tests\Unit\TestCase;
+
+class RegistrationGateTest extends TestCase
+{
+    private QuestionRepository $questions;
+    private AnswerRepository $answers;
+    private PolicyRepository $policies;
+    private PolicyVersionRepository $versions;
+    private AcceptanceRepository $acceptances;
+    private RegistrationGate $gate;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->questions   = Mockery::mock(QuestionRepository::class);
+        $this->answers     = Mockery::mock(AnswerRepository::class);
+        $this->policies    = Mockery::mock(PolicyRepository::class);
+        $this->versions    = Mockery::mock(PolicyVersionRepository::class);
+        $this->acceptances = Mockery::mock(AcceptanceRepository::class);
+
+        $this->gate = new RegistrationGate(
+            $this->questions,
+            $this->answers,
+            $this->policies,
+            $this->versions,
+            $this->acceptances
+        );
+    }
+
+    private function requiredQuestion(): Question
+    {
+        return new Question(offeringId: 7, label: 'Level?', isRequired: true, id: 3);
+    }
+
+    private function bookingPolicy(): Policy
+    {
+        return new Policy('Cancellation', 'cancellation', currentVersionId: 9, acceptanceScope: Policy::SCOPE_BOOKING, id: 1);
+    }
+
+    public function testValidatePassesWhenAnswersAndPoliciesProvided(): void
+    {
+        $this->questions->shouldReceive('findByOffering')->with(7, true)->andReturn([$this->requiredQuestion()]);
+        $this->policies->shouldReceive('findForScope')->with(Policy::SCOPE_BOOKING)->andReturn([$this->bookingPolicy()]);
+        $this->versions->shouldReceive('findById')->with(9)->andReturn(new PolicyVersion(1, 1, 'body', PolicyVersion::STATUS_PUBLISHED, null, 9));
+
+        self::assertNull($this->gate->validate(7, [3 => 'Beginner'], [9]));
+    }
+
+    public function testValidateFailsWhenRequiredQuestionUnanswered(): void
+    {
+        $this->questions->shouldReceive('findByOffering')->with(7, true)->andReturn([$this->requiredQuestion()]);
+
+        $result = $this->gate->validate(7, [3 => '   '], [9]);
+
+        self::assertInstanceOf(\WP_Error::class, $result);
+        self::assertSame('missing_answer', $result->get_error_code());
+    }
+
+    public function testValidateFailsWhenPolicyNotAccepted(): void
+    {
+        $this->questions->shouldReceive('findByOffering')->with(7, true)->andReturn([$this->requiredQuestion()]);
+        $this->policies->shouldReceive('findForScope')->with(Policy::SCOPE_BOOKING)->andReturn([$this->bookingPolicy()]);
+        $this->versions->shouldReceive('findById')->with(9)->andReturn(new PolicyVersion(1, 1, 'body', PolicyVersion::STATUS_PUBLISHED, null, 9));
+
+        $result = $this->gate->validate(7, [3 => 'Beginner'], []);
+
+        self::assertInstanceOf(\WP_Error::class, $result);
+        self::assertSame('policy_required', $result->get_error_code());
+    }
+
+    public function testRecordPersistsAnswersAndAcceptances(): void
+    {
+        $this->questions->shouldReceive('findByOffering')->with(7, true)->andReturn([$this->requiredQuestion()]);
+        $this->policies->shouldReceive('findForScope')->with(Policy::SCOPE_BOOKING)->andReturn([$this->bookingPolicy()]);
+        $this->versions->shouldReceive('findById')->with(9)->andReturn(new PolicyVersion(1, 1, 'body', PolicyVersion::STATUS_PUBLISHED, null, 9));
+
+        $this->answers->shouldReceive('insert')
+            ->once()
+            ->with(Mockery::on(static fn (Answer $a): bool => $a->questionId === 3 && $a->registrationId === 50 && $a->answerValue === 'Beginner'));
+
+        $this->acceptances->shouldReceive('insert')
+            ->once()
+            ->with(Mockery::on(static fn (PolicyAcceptance $a): bool => $a->policyVersionId === 9 && $a->registrationType === PolicyAcceptance::REG_LESSON && $a->registrationId === 50));
+
+        $this->gate->record(PolicyAcceptance::REG_LESSON, 50, 5, 7, [3 => 'Beginner'], [9], '203.0.113.7');
+    }
+}