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/subscription/checkout-screen.tsx

@@ -4,6 +4,7 @@ import { useEffect, useMemo, useState } from "react";
 import { useSearchParams } from "next/navigation";
 import { useQuery, useMutation } from "@tanstack/react-query";
 import { useTranslations } from "next-intl";
+import { useApiError } from "@/lib/use-api-error";
 import { useRouter } from "@/i18n/routing";
 import { ArrowRight, ArrowLeft, ShieldCheck } from "lucide-react";
 import { apiGet, apiPost } from "@/lib/api/client";
@@ -34,6 +35,7 @@ export function CheckoutScreen() {
   const t = useTranslations("subscription");
   const tc = useTranslations("subscription.checkout");
   const tPlans = useTranslations("settings.plans");
+  const apiError = useApiError();
   const searchParams = useSearchParams();
   const router = useRouter();
   const user = useAuthStore((s) => s.user);
@@ -81,8 +83,7 @@ export function CheckoutScreen() {
       window.location.href = data.paymentUrl;
     },
     onError: (err: unknown) => {
-      const msg = err instanceof Error ? err.message : String(err);
-      setPayError(msg || tc("paymentFailed"));
+      setPayError(apiError(err, tc("paymentFailed")));
     },
   });