feat: i18n system, lang switch component, english subtitles, UI improvements, roadmap update

src/components/LangSwitch.vue

@@ -0,0 +1,41 @@
+<script setup lang="ts">
+import { useI18n } from '@/composables/useI18n'
+
+const { currentLang, setLang, t } = useI18n()
+</script>
+
+<template>
+  <div class="lang-switch">
+    <button
+      :class="['lang-btn', { active: currentLang === 'zh' }]"
+      @click="setLang('zh')"
+    >中文</button>
+    <button
+      :class="['lang-btn', { active: currentLang === 'en' }]"
+      @click="setLang('en')"
+    >English</button>
+  </div>
+</template>
+
+<style scoped>
+.lang-switch {
+  display: flex;
+  gap: 2px;
+}
+
+.lang-btn {
+  padding: 4px 10px;
+  font-size: 12px;
+  color: #888;
+  background: rgba(255, 255, 255, 0.05);
+  border: 1px solid rgba(255, 255, 255, 0.1);
+  cursor: pointer;
+  transition: all 0.15s;
+}
+
+.lang-btn:first-child { border-radius: 3px 0 0 3px; }
+.lang-btn:last-child { border-radius: 0 3px 3px 0; }
+
+.lang-btn:hover { color: #ccc; background: rgba(255, 255, 255, 0.1); }
+.lang-btn.active { color: #fff; background: rgba(255, 255, 255, 0.15); border-color: rgba(255, 255, 255, 0.25); }
+</style>