add composer-unused, comprehensive docs, and project restructure

- Add icanhazstring/composer-unused as dev dependency for dependency hygiene checks
- Add German documentation (docs/) covering architecture, conventions, workflows, and developer checklists
- Add API layer (ApiAuth, ApiBootstrap, ApiResponse), audit, scheduler, custom fields, and SSO services
- Add Microsoft OIDC SSO, API token management, and user lifecycle features
- Add swagger-ui vendor integration and OpenAPI spec
- Add production Docker setup and bin/ scripts
- Update composer dependencies, config, templates, and frontend assets throughout

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pages/error/forbidden(error).phtml

@@ -2,13 +2,12 @@
 
 use MintyPHP\Http\Request;
 
-header('HTTP/1.1 403 Forbidden');
+http_response_code(403);
 
-$path = Request::pathWithQuery();
+$path = Request::safeReturnTarget($_GET['url'] ?? '');
 $pathDisplay = $path === '' ? '/' : '/' . $path;
 $home = lurl('');
-$backTarget = Request::safeReturnTarget('');
-$backUrl = $backTarget !== '' ? lurl($backTarget) : $home;
+$backUrl = $path !== '' ? lurl($path) : $home;
 
 ?>
 <header>