feat: 集成豆包 ASR 语音识别后端，支持 /voice doubao 切换 (#357)

* feat: 集成豆包 ASR 语音识别后端，支持 /voice doubao 切换

- 新增 src/services/doubaoSTT.ts 适配模块，将 doubaoime-asr 的
  AsyncGenerator 协议适配为现有 VoiceStreamConnection 接口
- /voice doubao 启用豆包后端，/voice 使用默认 Anthropic 后端
- 后端选择持久化到 settings.json 的 voiceProvider 字段
- 豆包后端跳过 Anthropic OAuth 认证、语言限制和 Focus Mode
- 豆包后端松手即出结果，跳过 processing 状态
- 凭证文件存放在 ~/.claude/tts/doubao/credentials.json
- doubaoime-asr 作为 optionalDependencies 安装
- 移除 /voice 命令的 claude-ai 可用性限制，所有用户可用

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* docs: 更新 Voice Mode 文档，添加豆包 ASR 后端说明和致谢

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

package.json

@@ -205,5 +205,8 @@
     "xss": "^1.0.15",
     "yaml": "^2.8.3",
     "zod": "^4.3.6"
+  },
+  "optionalDependencies": {
+    "doubaoime-asr": "^0.1.0"
   }
 }