feat(admin-i18n): add cookie-based locale runtime and switcher baseline

apps/admin/src/providers/admin-i18n-provider.tsx

@@ -0,0 +1,53 @@
+"use client"
+
+import type { AppLocale } from "@cms/i18n"
+import { createContext, type ReactNode, useContext, useMemo } from "react"
+
+import type { AdminMessages } from "@/i18n/messages"
+import { translateMessage } from "@/i18n/messages"
+
+type AdminI18nContextValue = {
+  locale: AppLocale
+  messages: AdminMessages
+}
+
+const AdminI18nContext = createContext<AdminI18nContextValue | null>(null)
+
+export function AdminI18nProvider({
+  locale,
+  messages,
+  children,
+}: {
+  locale: AppLocale
+  messages: AdminMessages
+  children: ReactNode
+}) {
+  const value = useMemo(
+    () => ({
+      locale,
+      messages,
+    }),
+    [locale, messages],
+  )
+
+  return <AdminI18nContext.Provider value={value}>{children}</AdminI18nContext.Provider>
+}
+
+export function useAdminI18n(): AdminI18nContextValue {
+  const context = useContext(AdminI18nContext)
+
+  if (!context) {
+    throw new Error("useAdminI18n must be used inside AdminI18nProvider")
+  }
+
+  return context
+}
+
+export function useAdminT() {
+  const { messages } = useAdminI18n()
+
+  return useMemo(
+    () => (key: string, fallback?: string) => translateMessage(messages, key, fallback),
+    [messages],
+  )
+}