feat(locale): persist household and member preferences

packages/domain/src/locale.ts

@@ -0,0 +1,14 @@
+export const SUPPORTED_LOCALES = ['en', 'ru'] as const
+
+export type SupportedLocale = (typeof SUPPORTED_LOCALES)[number]
+
+export function normalizeSupportedLocale(value?: string | null): SupportedLocale | null {
+  const normalized = value?.trim().toLowerCase()
+  if (!normalized) {
+    return null
+  }
+
+  return (SUPPORTED_LOCALES as readonly string[]).includes(normalized)
+    ? (normalized as SupportedLocale)
+    : null
+}