feat(core): generic CSV export primitive + helpdesk domains consumer

Add a reusable CSV-export building block to the core so any Grid.js list
page can gain a filter/sort-aware download with two clicks of glue.

Core primitive:
- core/Service/Export/CsvExportService: flavor-aware writer (plain CSV
  or Excel-compatible UTF-8+BOM+semicolon), with OWASP-aligned formula-
  injection escape (=, @, +, -, TAB, CR) applied to both rows *and*
  headers. Value objects for columns (ExportColumn) carry an extractor
  closure and an allowSignedNumeric flag for phone-number-shaped cells.
- core/Support/helpers/export.php: thin HTTP layer (exportSendCsv,
  exportCapLimit, exportResolveFlavor, exportRequireGetRequest) reusing
  the requestInput() contract for GR-CORE-003 consistency. Filename is
  sanitized and length-clamped; callers must still enforce auth.
- templates/partials/app-list-export-dropdown.phtml: zero-config
  <details class="dropdown"> with CSV + Excel triggers.
- web/js/core/app-list-export.js: initListExport({ gridConfig, exportUrl })
  mirrors the current grid filters + sort onto the export URL and
  navigates, preserving session cookies for download.

First consumer — Helpdesk domains:
- DomainListService extracts the shared filter/enrich/sort logic from
  domains-data so the grid endpoint and the new domains/export endpoint
  cannot drift.
- domains/export endpoint delegates to DomainListService, declares
  ExportColumns (with translated level labels), and exits via
  exportSendCsv.
- domains-data now ~20 lines, delegating to DomainListService.

Tests:
- CsvExportServiceTest (10 cases): both flavors, BOM/no-BOM, formula
  escapes incl. TAB/CR, header escape, signed-numeric allowlist,
  quoting, multiline, empty columns, generator-compatible iterable.
- ExportHelpersTest (5 cases): exportCapLimit bounds.
- DomainListServiceTest (8 cases): filter, search, "all" sentinel,
  sort, paging, enrichment, BC failure, tenant-scoped security filter.

Gates: PHPUnit green, PHPStan clean on touched files, module:sync ok.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

modules/helpdesk/lib/Module/Helpdesk/HelpdeskContainerRegistrar.php

@@ -10,6 +10,7 @@ use MintyPHP\Module\Helpdesk\Service\BcSoapGateway;
 use MintyPHP\Module\Helpdesk\Service\DebitorDetailService;
 use MintyPHP\Module\Helpdesk\Service\DebitorSearchService;
 use MintyPHP\Module\Helpdesk\Service\DomainDetailService;
+use MintyPHP\Module\Helpdesk\Service\DomainListService;
 use MintyPHP\Module\Helpdesk\Service\EffectiveHelpdeskSettingsService;
 use MintyPHP\Module\Helpdesk\Service\HelpdeskOAuthTokenService;
 use MintyPHP\Module\Helpdesk\Service\HelpdeskSettingsGateway;
@@ -127,6 +128,11 @@ final class HelpdeskContainerRegistrar implements ContainerRegistrar
             $c->get(DomainSecurityLevelRepository::class)
         ));
 
+        $container->set(DomainListService::class, static fn (AppContainer $c): DomainListService => new DomainListService(
+            $c->get(BcODataGateway::class),
+            $c->get(DomainSecurityLevelService::class)
+        ));
+
         $container->set(HandoverRepository::class, static fn (): HandoverRepository => new HandoverRepository());
 
         $container->set(HandoverRevisionRepository::class, static fn (): HandoverRevisionRepository => new HandoverRevisionRepository());