fix(audit): harden module isolation and fix post-extraction drift

Fix 5 broken FQCN references (runtime errors) where core pages referenced
non-existent MintyPHP\Service\Audit\AuditMetadataEnricher and SystemAuditService.
Add AuditMetadataEnricherInterface with NullAuditMetadataEnricher fallback so
deactivating the audit module no longer crashes core edit pages.

Move audit search resources from core Search*Provider files into the module
via a new AuditSearchResourceProvider implementing the existing
SearchResourceProvider contract. Add module-specific purge permissions
(audit.api.purge, audit.imports.purge) replacing core ABILITY_ADMIN_SETTINGS_UPDATE.

Also fixes: session key prefix convention, hardcoded English string, $_SERVER
superglobal fallback, and manifest schema drift (i18n_path, group in ui_slots).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/Service/Audit/AuditMetadataEnricherInterface.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace MintyPHP\Service\Audit;
+
+/**
+ * Core-side contract for enriching entity audit metadata (created_by, modified_by, etc.)
+ * with user display labels and UUIDs.
+ *
+ * Implemented by the audit module's AuditMetadataEnricher when the module is active.
+ * Falls back to NullAuditMetadataEnricher (no-op) when the audit module is disabled.
+ */
+interface AuditMetadataEnricherInterface
+{
+    /**
+     * Resolve audit user IDs on an entity into display labels and UUIDs.
+     *
+     * @param array<string,mixed> $entity The entity array (modified in place).
+     * @param list<string>        $fields Audit field names to resolve (e.g. 'created_by', 'modified_by').
+     */
+    public function enrich(array &$entity, array $fields = ['created_by', 'modified_by']): void;
+}