Add Policies domain (drafting, versioning, tracked acceptance)

Implements #6: studio admins draft, version, and publish policies; the
public registration gate reads the current published version of each, and
acceptance is recorded against the exact version so a new version must be
re-accepted at the next booking.

- src/Policy/: Policy, PolicyVersion, PolicyAcceptance value objects;
  PolicyRepository, PolicyVersionRepository, AcceptanceRepository;
  PolicyService (orchestrates create/add-draft/publish across the policies
  and versions tables); PolicyEndpoint (REST); PolicyController +
  templates/admin/policies.php (Policies admin menu, manage_policies)
- us_policies, us_policy_versions, us_policy_acceptances tables in Schema
- REST: public GET /policies (current published versions); manage_policies
  for create, add version, edit draft, and publish
- Wiring in Plugin, RestRegistrar, AdminMenu

AcceptanceRepository is built now and consumed by the booking/enrolment
gate in #3/#4.

Also bump PHPStan to --memory-limit=1G in the composer lint script; the
default 128M now crashes the analysis as the codebase has grown.

Tests: tests/Unit/Policy/ (value objects, repositories, service).
composer test (90 total), cs, and PHPStan level 6 all pass.

Refs #6

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

src/Policy/AcceptanceRepository.php

@@ -0,0 +1,57 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Policy;
+
+class AcceptanceRepository {
+
+	private string $table;
+
+	public function __construct( private \wpdb $db ) {
+		$this->table = $db->prefix . 'us_policy_acceptances';
+	}
+
+	public function insert( PolicyAcceptance $acceptance ): int {
+		$this->db->insert(
+			$this->table,
+			[
+				'policy_version_id' => $acceptance->policyVersionId,
+				'student_id'        => $acceptance->studentId,
+				'registration_type' => $acceptance->registrationType,
+				'registration_id'   => $acceptance->registrationId,
+				'ip_address'        => $acceptance->ipAddress,
+				'accepted_at'       => current_time( 'mysql' ),
+			],
+			[ '%d', '%d', '%s', '%d', '%s', '%s' ]
+		);
+
+		return $this->db->insert_id;
+	}
+
+	/**
+	 * Persist a batch of acceptances for a single registration.
+	 *
+	 * @param list<PolicyAcceptance> $acceptances
+	 * @return list<int> Inserted acceptance IDs.
+	 */
+	public function insertMany( array $acceptances ): array {
+		return array_map( fn( PolicyAcceptance $a ): int => $this->insert( $a ), $acceptances );
+	}
+
+	/**
+	 * Find all acceptances attached to a registration (lesson or enrolment).
+	 *
+	 * @return list<PolicyAcceptance>
+	 */
+	public function findByRegistration( string $registrationType, int $registrationId ): array {
+		$rows = $this->db->get_results(
+			$this->db->prepare(
+				"SELECT * FROM {$this->table} WHERE registration_type = %s AND registration_id = %d ORDER BY id ASC",
+				$registrationType,
+				$registrationId
+			)
+		);
+
+		return array_map( PolicyAcceptance::fromRow( ... ), $rows ?? [] );
+	}
+}