fix : 언어팩 추가 및 내용 추가

lang/en/error.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * System/Domain error messages (client-facing, fixed strings)
+ * - Not DB-driven
+ * - Used in global handler/service exceptions
+ * - Example: throw new NotFoundHttpException(__('error.not_found'));
+ */
+return [
+
+    // 4xx Common
+    'not_found'        => 'The requested URI or data was not found.', // 404
+    'tenant_id'        => 'No active tenant is set.',                 // 400 (Service::tenantId() missing)
+    'unauthenticated'  => 'Authentication failed.',                   // 401
+    'forbidden'        => 'You do not have permission for this request.', // 403
+    'bad_request'      => 'Invalid request.',                         // 400
+
+    // Validation / Parameters
+    'validation_failed' => 'Request data validation failed.',         // 422
+    'missing_parameter' => 'A required parameter is missing.',        // 400
+
+    // Resource-specific (optional, with :resource placeholder)
+    'not_found_resource' => ':resource could not be found.',          // 404
+
+    // Business rules
+    'duplicate'       => 'Duplicate data exists.',
+    'conflict'        => 'The request conflicts with the current state.', // 409
+    'state_invalid'   => 'The current state does not allow this operation.', // 400/409
+
+    // Server errors
+    'server_error'    => 'An internal server error occurred.',        // 5xx
+
+];