feat: internationalize API error responses by locale

Add shared error codes with zh/en/ms messages, coded app exceptions,
and locale-aware global filter. Frontends send X-Locale so error text
matches the active UI language.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/shared/common/app-error.ts

@@ -0,0 +1,45 @@
+import {
+  BadRequestException,
+  ForbiddenException,
+  NotFoundException,
+  UnauthorizedException,
+} from '@nestjs/common';
+import type { ApiErrorCode, ApiErrorParams } from '@thebet365/shared';
+
+function body(code: ApiErrorCode, params?: ApiErrorParams) {
+  const clean = params
+    ? Object.fromEntries(
+        Object.entries(params)
+          .filter(([, v]) => v !== undefined && v !== null)
+          .map(([k, v]) => [k, String(v)]),
+      )
+    : undefined;
+  return { code, params: clean };
+}
+
+export function appBadRequest(code: ApiErrorCode, params?: ApiErrorParams) {
+  return new BadRequestException(body(code, params));
+}
+
+export function appNotFound(code: ApiErrorCode, params?: ApiErrorParams) {
+  return new NotFoundException(body(code, params));
+}
+
+export function appForbidden(code: ApiErrorCode, params?: ApiErrorParams) {
+  return new ForbiddenException(body(code, params));
+}
+
+export function appUnauthorized(code: ApiErrorCode, params?: ApiErrorParams) {
+  return new UnauthorizedException(body(code, params));
+}
+
+export function isCodedExceptionResponse(
+  res: unknown,
+): res is { code: ApiErrorCode; params?: ApiErrorParams } {
+  return (
+    typeof res === 'object' &&
+    res !== null &&
+    'code' in res &&
+    typeof (res as { code: unknown }).code === 'string'
+  );
+}