Voice mode: option to auto-submit on space bar release

Feature request

When using voice mode (hold Space to record), it would be great to have an option to automatically submit the transcribed message as soon as the space bar is released, rather than requiring a separate Enter press.

Current behavior

1. Hold Space to record
2. Release Space → transcription appears in the input
3. Press Enter to submit

Desired behavior

An opt-in setting (e.g., voiceAutoSubmit: true in settings or a keybinding config) that changes step 3 to happen automatically after transcription completes.

Motivation

When using voice mode conversationally, the extra Enter press breaks the flow. Auto-submit would make voice interactions feel more natural and hands-free.