feat：语音对话优化

frontend/src/lib/i18n/zh-CN.ts

@@ -54,6 +54,8 @@ export const zhCN: TranslationMap = {
   "chat.title": "对话",
   "chat.mode.observation": "观察模式",
   "chat.reconnecting": "连接已断开，正在重连...",
+  "chat.connecting": "正在连接服务...",
+  "chat.vadInit": "正在初始化语音检测...",
   "chat.empty.prompt": "在下方输入文字开始对话",
   "chat.empty.hint": "输入文字即可与 AI 交互，也可点击左侧按钮开启视频",
   "chat.welcome.prompt": "在下方输入文字开始对话",
@@ -65,6 +67,7 @@ export const zhCN: TranslationMap = {
   // Session messages
   "session.changeDetected": "👁️ 画面变化检测",
   "session.recognizing": "（语音识别中...）",
+  "session.sttFailed": "（语音识别失败，请重试）",
   "session.noSpeech": "（未识别到语音）",
   "session.interrupted": "（已打断）",