fix(conversation): 离屏不丢回复、列表预热 WS 与非阻塞进入聊天

- 后端：文本/转写后 AI 生成改为独立任务，避免断连取消整轮；按需 TTS 等与 WS 改动
- 前端：RealtimeSession 重绑 UI 时恢复流式 buffer；列表 onPressIn/挂载预热、已有会话立即 push
- 同步会话相关类型、i18n、测试与 env/资源等累计改动

Co-authored-by: Cursor <cursoragent@cursor.com>

app-expo/src/i18n/locales/en/conversation.json

@@ -29,10 +29,15 @@
   "readAloudAgain": "Play again",
   "readAloudPause": "Pause reading",
   "readAloudResume": "Resume reading",
+  "readAloudRequest": "Read aloud",
+  "readAloudRequestFailed": "Could not start playback. Check your connection.",
+  "readAloudNoMessageId": "This message is not ready for on-demand reading yet. Pull to refresh or try again.",
   "cannotReadAloud": "Read unavailable",
   "readingAloud": "Reading aloud…",
   "recordingPermissionDenied": "Microphone permission is required to record",
   "recordingStartFailed": "Unable to start recording. Please try again.",
+  "ttsThisTurn": "Speak",
+  "ttsThisTurnAccessibility": "When on, assistant replies synthesize speech before text appears.",
   "send": "Send",
   "startNewSubtitle": "Capture a new memory or share your thoughts with your companion.",
   "switchToText": "Switch to text input",