Voice mode: auto-submit on spacebar release (PTT send)

## Feature Request

### Summary
When using voice mode (push-to-talk with spacebar), automatically submit the transcribed text when the spacebar is released — without requiring a separate Enter key press.

### Current behavior
- Hold Space → records audio
- Release Space → transcription appears in input box
- User must press Enter manually to submit

### Desired behavior
- Hold Space → records audio
- Release Space → transcription appears **and is automatically submitted**

### Why
This would make the voice workflow fully hands-free. Currently the required Enter press breaks the flow, especially when the hands are away from the keyboard during dictation.

### Suggested implementation
Add a setting (e.g. \oice.autoSubmitOnRelease: true\) that sends Enter immediately after transcription is inserted on spacebar release.

未指定文件或测试。首先定位 voice-mode 的空格键释放处理程序、转录插入流程，以及可能的自动提交设置的配置路径。完成的标准是，释放 push-to-talk 音频后，其转录内容会被插入并自动提交，同时该设置控制这一行为。

由索引模型根据 Issue 内容生成。