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/PolicyVersion.php

@@ -0,0 +1,58 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Policy;
+
+class PolicyVersion {
+
+	public const STATUS_DRAFT     = 'draft';
+	public const STATUS_PUBLISHED = 'published';
+	public const STATUS_ARCHIVED  = 'archived';
+
+	/**
+	 * All valid version statuses.
+	 *
+	 * @var list<string>
+	 */
+	public const VALID_STATUSES = [ self::STATUS_DRAFT, self::STATUS_PUBLISHED, self::STATUS_ARCHIVED ];
+
+	public function __construct(
+		public readonly int $policyId,
+		public readonly int $versionNumber,
+		public readonly ?string $body = null,
+		public readonly string $status = self::STATUS_DRAFT,
+		public readonly ?string $publishedAt = null,
+		public readonly ?int $id = null,
+	) {}
+
+	public static function fromRow( object $row ): self {
+		return new self(
+			policyId:      (int) $row->policy_id,
+			versionNumber: (int) $row->version_number,
+			body:          $row->body,
+			status:        $row->status,
+			publishedAt:   $row->published_at,
+			id:            (int) $row->id,
+		);
+	}
+
+	public function isPublished(): bool {
+		return self::STATUS_PUBLISHED === $this->status;
+	}
+
+	/**
+	 * Returns a plain array representation of the version.
+	 *
+	 * @return array<string, mixed>
+	 */
+	public function toArray(): array {
+		return [
+			'id'             => $this->id,
+			'policy_id'      => $this->policyId,
+			'version_number' => $this->versionNumber,
+			'body'           => $this->body,
+			'status'         => $this->status,
+			'published_at'   => $this->publishedAt,
+		];
+	}
+}