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>

lib/Service/Access/UiCapabilityMap.php

@@ -29,6 +29,7 @@ final class UiCapabilityMap
         'can_view_imports_audit' => OperationsAuthorizationPolicy::ABILITY_ADMIN_IMPORTS_AUDIT_VIEW,
         'can_view_user_lifecycle_audit' => OperationsAuthorizationPolicy::ABILITY_ADMIN_USER_LIFECYCLE_AUDIT_VIEW,
         'can_view_stats' => OperationsAuthorizationPolicy::ABILITY_ADMIN_STATS_VIEW,
+        'can_view_system_info' => OperationsAuthorizationPolicy::ABILITY_ADMIN_SYSTEM_INFO_VIEW,
     ];
 
     /**