[Bug] Extra space

## Bug Report

### Description
When I press 'Tab', a space is introduced before the text completion.

### Expected Behavior
No initial space

### Environment
- **Cotabby version:** 0.4.2-beta
- **macOS version:** 26.6
- **Mac model:** Mac16,8
- **Chip:** Apple M4 Pro
- **Memory:** 24 GB

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*Submitted via tabby feedback form*