feat: i18n — EN/MS/ZH translations with cookie-based locale switching, report form translated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FFDuBhMKvoWjrWT3ZnGmmr

lib/i18n/context.tsx

@@ -0,0 +1,24 @@
+'use client'
+
+import { createContext, useContext } from 'react'
+import type en from '../../messages/en.json'
+
+export type Messages = typeof en
+
+const I18nContext = createContext<Messages | null>(null)
+
+export function I18nProvider({
+  messages,
+  children,
+}: {
+  messages: Messages
+  children: React.ReactNode
+}) {
+  return <I18nContext.Provider value={messages}>{children}</I18nContext.Provider>
+}
+
+export function useTranslations<K extends keyof Messages>(namespace: K): Messages[K] {
+  const ctx = useContext(I18nContext)
+  if (!ctx) throw new Error('useTranslations must be used inside I18nProvider')
+  return ctx[namespace]
+}