Voice mode: add auto-submit option after transcription

Feature request

Add an option to automatically submit the prompt after voice transcription completes, without needing to press Enter.

Current behavior

1. Hold Space to record
2. Release to finalize transcription
3. Text is inserted into the prompt
4. Must manually press Enter to submit

Desired behavior

A setting (e.g. voiceAutoSubmit: true) that automatically sends the prompt once transcription is finalized, enabling a fully hands-free workflow.

The default could remain as-is (manual Enter) for users who want to review/edit before sending.

Use case

When using voice mode for quick prompts, the extra Enter keypress breaks the flow. An auto-submit option would make voice interaction feel more natural and hands-free.