fix(i18n): localize API error messages by code (no more raw English)

Error toasts surfaced the raw English backend message. Added an errors namespace (fa/ar/en) keyed by error code + a useApiError() resolver that maps ApiClientError.code to the localized message (fallback to a localized generic). Wired into menu, tables, demo banner, and subscription checkout; hardened getErrorMessage so it never returns the raw backend message.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/dashboard/src/components/demo/demo-data-banner.tsx

@@ -3,8 +3,9 @@
 import { useState } from "react";
 import { useMutation, useQueryClient } from "@tanstack/react-query";
 import { Sparkles, Loader2 } from "lucide-react";
-import { ApiClientError, apiPost } from "@/lib/api/client";
+import { apiPost } from "@/lib/api/client";
 import { notify } from "@/lib/notify";
+import { useApiError } from "@/lib/use-api-error";
 import { useAuthStore } from "@/lib/stores/auth.store";
 import { Button } from "@/components/ui/button";
 import { cn } from "@/lib/utils";
@@ -27,6 +28,7 @@ export function DemoDataBanner({ invalidateKeys, className }: Props) {
   const cafeId = useAuthStore((s) => s.user?.cafeId);
   const role = useAuthStore((s) => s.user?.role);
   const qc = useQueryClient();
+  const apiError = useApiError();
   const [done, setDone] = useState(false);
   const [summary, setSummary] = useState<DemoSeedResult | null>(null);
 
@@ -41,11 +43,7 @@ export function DemoDataBanner({ invalidateKeys, className }: Props) {
       }
     },
     onError: (err) => {
-      notify.error(
-        err instanceof ApiClientError
-          ? err.message
-          : "افزودن داده‌های نمونه ناموفق بود. دوباره تلاش کنید."
-      );
+      notify.error(apiError(err));
     },
   });