docs(agents): encode list-export convention as GR-UI-EXPORT guard

Make the core-primitive-end-to-end rule for Grid.js list exports binding
instead of advisory — so future consumers (and reviewers) cannot quietly
drift back into inline fputcsv / hand-rolled headers / bespoke click
listeners / lurl() for query-carrying URLs.

- CLAUDE.md: new UI Patterns bullet + two "Never Do This" entries
  spelling out the server/view/client contract in one place.
- .agents/checks/guard-catalog.json: new GR-UI-EXPORT entry describing
  the end-to-end requirement (exportRequireGetRequest + exportCapLimit +
  exportSendCsv + ExportColumn + shared filter-schema + dropdown partial
  + endpointUrl() + initListExport).
- .agents/checks/guard-enforcement-map.json: wire the new guard to
  tests/Architecture/ListExportContractTest.php as the automated
  evidence source.
- .agents/checks/guard-checklist.md & .agents/prompts/reviewer-code.md:
  add GR-UI-EXPORT so the Code Reviewer prompt and the checklist flag
  violations alongside GR-UI-LIST.
- tests/Architecture/ListExportContractFiles: registry of every list
  export (currently helpdesk-domains, admin/users, audit/system-audit).
  Adding a new list = one entry, contract test covers the rest.
- tests/Architecture/ListExportContractTest: six checks per registered
  entry — endpoint uses the primitive, no hand-rolled output, data and
  export share the same filter-schema, template includes the dropdown
  partial and uses endpointUrl(), page module imports and invokes
  initListExport, and the shared dropdown partial stays zero-config.
- pages/admin/users/export().php: align with the new contract by
  switching from ad-hoc requestInput()->queryAll() reads to
  gridParseFiltersFromSchemaFile(__DIR__ . '/filter-schema.php'), same
  as the data endpoint — eliminates the last place Grid and export
  could disagree on what "the current filter" means.

Gates: PHPUnit 1900 OK (+6 contract checks), PHPStan 0 errors.

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

CLAUDE.md

@@ -171,6 +171,10 @@ docker/                 # Dockerfiles, Nginx configs, PHP configs
 - **Components inside forms**: Reset core `margin-bottom` on buttons/inputs/selects/labels at component scope. Checkboxes in flex need explicit `1.25em` sizing + `flex-shrink: 0`.
 - **Sticky elements**: Always use `top: calc(var(--app-topbar-height) + ...)` — never `top: 0`. Multi-column grids must have a responsive single-column `@media` fallback.
 - **File uploads** use `app-file-upload.phtml` partial (deliberate exception to plain-HTML inputs — the markup is too complex for inline use). See `templates/partials/app-file-upload.phtml` for the `$fileUpload` array contract. Never write file-upload markup inline; always use the partial.
+- **List exports**: every Grid.js list that offers a download MUST go through the core primitive — no inline `fputcsv`, no hand-rolled headers, no bespoke dropdown. (GR-UI-EXPORT)
+  - **Server:** endpoint calls `exportRequireGetRequest()` + `exportCapLimit()` + `exportSendCsv()` from `core/Support/helpers/export.php`, builds columns as `ExportColumn[]` (`core/Service/Export/CsvExportService.php`), and reuses the SAME `filter-schema.php` via `gridParseFiltersFromSchemaFile()` as the data endpoint. Extract a shared service or presenter if row-formatting is non-trivial (see `DomainListService` / `SystemAuditRowPresenter`).
+  - **View:** `require templatePath('partials/app-list-export-dropdown.phtml');` inside `$listTitleActionsHtml`. Pass the URL via `'exportUrl' => endpointUrl('<route-path>')` in the page config — **always `endpointUrl()`, never plain `lurl()`**. The helper resolves module routes to their target path so query strings survive.
+  - **Client:** `initListExport({ gridConfig, exportUrl })` from `/js/core/app-list-export.js`. No hand-rolled click listener, no inline URL construction.
 
 ### Never Do This
 
@@ -186,6 +190,8 @@ docker/                 # Dockerfiles, Nginx configs, PHP configs
 - Inline SQL or string-concatenated queries (GR-SEC-003)
 - Raw `echo` in views without `// raw-html-ok` marker — use `e()` (GR-SEC-010)
 - OpenAPI changes without updating the spec (GR-CORE-007)
+- Hand-rolled list exports (inline `fputcsv`, own header setup, bespoke click-to-download JS) — always use `core/Service/Export/*` + `exportSendCsv()` + `app-list-export-dropdown.phtml` + `initListExport()` (GR-UI-EXPORT)
+- Building an export/data endpoint URL with `lurl()` when it will carry query params — use `endpointUrl()` so module routes where `path ≠ target` still resolve (GR-UI-EXPORT)
 
 ## Database