feat(i18n): add AI history components internationalization support

- Add useI18n composable and ai-history locale files
- Refactor 10 AI history Vue components to support i18n (GPTEvolutionDemo, AIErasComparisonDemo, AiEvolutionDemo, etc.)
- Add English version of AI history appendix article
- Add English translations for stage-1 appendix-articles:
  - vibe-coding-tools-snake-game-tutorial.md
  - vibe-coding-tools-build-website-with-ai-coding-and-design-agents.md
- Use relative paths to reference Chinese version images
- Update appendix sidebar config to use English AI history link

docs/.vitepress/theme/composables/useI18n.js

@@ -0,0 +1,44 @@
+import { computed } from 'vue'
+import { useData } from 'vitepress'
+
+const langMap = {
+  'zh-CN': 'zh-cn',
+  'en-US': 'en',
+  'ja-JP': 'ja-jp',
+  'zh-TW': 'zh-tw',
+  'ko-KR': 'ko-kr',
+  'es-ES': 'es-es',
+  'fr-FR': 'fr-fr',
+  'de-DE': 'de-de',
+  'ar-SA': 'ar-sa',
+  'vi-VN': 'vi-vn'
+}
+
+/**
+ * Lightweight i18n composable for VitePress Vue components.
+ *
+ * @param {Record<string, Record<string, any>>} messages
+ *   Locale map, e.g. { 'zh-cn': { title: '标题' }, en: { title: 'Title' } }
+ * @returns {{ t: (key: string) => any, locale: import('vue').ComputedRef<string> }}
+ */
+export function useI18n(messages) {
+  const { lang } = useData()
+
+  const locale = computed(() => langMap[lang.value] || 'zh-cn')
+
+  const current = computed(
+    () => messages[locale.value] || messages['zh-cn'] || {}
+  )
+
+  const t = (key) => {
+    const keys = key.split('.')
+    let val = current.value
+    for (const k of keys) {
+      val = val?.[k]
+      if (val === undefined) return key
+    }
+    return val
+  }
+
+  return { t, locale, messages: current }
+}