feat(app): 按错误码展示中英印尼文案

lib/core/formatting/error_text.dart

@@ -2,14 +2,37 @@
 
 import '../../l10n/app_localizations.dart';
 
-const int _serverErrorCode = 500;
-
-/// 用户端不展示内部故障文案。500 与空提示改成可理解的说明，业务提示原样保留。
+/// 按后端 `ErrorCode` 取当前语言文案。未收录的业务码回退服务端 message。
 String userFacingApiMessage(AppLocalizations l10n, int code, String message) {
-  if (code >= _serverErrorCode || message.isEmpty) return l10n.authServerError;
+  final localized = _apiMessage(l10n, code);
+  if (localized != null) return localized;
+  if (message.isEmpty) return l10n.authServerError;
   return message;
 }
 
+/// 已定义错误码。500 用服务繁忙，不展示「系统异常」。
+String? _apiMessage(AppLocalizations l10n, int code) {
+  return switch (code) {
+    400 => l10n.apiErrorBadRequest,
+    401 => l10n.apiErrorUnauthorized,
+    403 => l10n.apiErrorForbidden,
+    404 => l10n.apiErrorNotFound,
+    429 => l10n.apiErrorTooManyRequests,
+    500 => l10n.authServerError,
+    100000 => l10n.apiErrorLoginFailed,
+    100001 => l10n.apiErrorAccountDisabled,
+    100002 => l10n.apiErrorCoinNotEnough,
+    100003 => l10n.apiErrorEpisodeUnavailable,
+    100004 => l10n.apiErrorEpisodeUnlocked,
+    100005 => l10n.apiErrorOrderInvalid,
+    100006 => l10n.apiErrorVipExpired,
+    200001 => l10n.apiErrorDataExists,
+    200002 => l10n.apiErrorDataNotFound,
+    200003 => l10n.apiErrorNotAllowed,
+    _ => null,
+  };
+}
+
 /// logic 里的错误在两种情况下是"哨兵值"：本地网络异常（读不到后端提示语）与
 /// 我们自己包装的失败。这里统一翻译成当前语言的文案；服务端给的中文提示原样展示。
 String errorText(AppLocalizations l10n, String? code, String fallback) {