feat: add read-only System Info admin page with health checks and module inventory

New page at /admin/system-info with three tabs:
- Overview: PHP version, SAPI, environment, 6 health checks (DB, schema,
  storage, RBAC baseline, admin role, scheduler heartbeat)
- Modules: table of active modules with version, dependencies, permission count
- Permissions: active/inactive counts and per-source breakdown

Gated behind new system_info.view permission assigned to Admin role.
No mutations — purely diagnostic/observability.

Includes SystemHealthService, SystemInfoService, SystemHealthRepository
with interface, DI registration, i18n keys (de+en), idempotent DB update
script, and 17 new PHPUnit tests.

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

pages/admin/system-info/index().php

@@ -0,0 +1,16 @@
+<?php
+
+use MintyPHP\Buffer;
+use MintyPHP\Service\Access\OperationsAuthorizationPolicy;
+use MintyPHP\Service\System\SystemInfoService;
+use MintyPHP\Support\Guard;
+
+Guard::requireAbilityOrForbidden(OperationsAuthorizationPolicy::ABILITY_ADMIN_SYSTEM_INFO_VIEW);
+
+$pageData = app(SystemInfoService::class)->buildPageData();
+$overview = $pageData['overview'] ?? [];
+$modules = $pageData['modules'] ?? [];
+$permissions = $pageData['permissions'] ?? [];
+$healthChecks = $overview['health_checks'] ?? [];
+
+Buffer::set('title', t('System Info'));