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/PolicyVersionRepository.php

@@ -0,0 +1,88 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Policy;
+
+class PolicyVersionRepository {
+
+	private string $table;
+
+	public function __construct( private \wpdb $db ) {
+		$this->table = $db->prefix . 'us_policy_versions';
+	}
+
+	public function insert( PolicyVersion $version ): int {
+		$this->db->insert(
+			$this->table,
+			[
+				'policy_id'      => $version->policyId,
+				'version_number' => $version->versionNumber,
+				'body'           => $version->body,
+				'status'         => $version->status,
+				'published_at'   => $version->publishedAt,
+				'created_at'     => current_time( 'mysql' ),
+			],
+			[ '%d', '%d', '%s', '%s', '%s', '%s' ]
+		);
+
+		return $this->db->insert_id;
+	}
+
+	public function updateBody( int $id, ?string $body ): bool {
+		return false !== $this->db->update(
+			$this->table,
+			[ 'body' => $body ],
+			[ 'id' => $id ],
+			[ '%s' ],
+			[ '%d' ]
+		);
+	}
+
+	public function updateStatus( int $id, string $status, ?string $publishedAt = null ): bool {
+		return false !== $this->db->update(
+			$this->table,
+			[
+				'status'       => $status,
+				'published_at' => $publishedAt,
+			],
+			[ 'id' => $id ],
+			[ '%s', '%s' ],
+			[ '%d' ]
+		);
+	}
+
+	/**
+	 * All versions of a policy, newest version number first.
+	 *
+	 * @return list<PolicyVersion>
+	 */
+	public function findByPolicy( int $policyId ): array {
+		$rows = $this->db->get_results(
+			$this->db->prepare(
+				"SELECT * FROM {$this->table} WHERE policy_id = %d ORDER BY version_number DESC",
+				$policyId
+			)
+		);
+
+		return array_map( PolicyVersion::fromRow( ... ), $rows ?? [] );
+	}
+
+	public function findById( int $id ): ?PolicyVersion {
+		$row = $this->db->get_row(
+			$this->db->prepare( "SELECT * FROM {$this->table} WHERE id = %d", $id )
+		);
+
+		return $row ? PolicyVersion::fromRow( $row ) : null;
+	}
+
+	/**
+	 * Highest version_number assigned for a policy (0 when none exist yet).
+	 */
+	public function maxVersionNumber( int $policyId ): int {
+		$max = $this->db->get_var(
+			$this->db->prepare( "SELECT MAX(version_number) FROM {$this->table} WHERE policy_id = %d", $policyId )
+		);
+
+		return null === $max ? 0 : (int) $max;
+	}
+}