Release v1.4.0

[skitsanos]

Summary

Release TranscribeIt v1.4.0.

Highlights

• Add Gemini transcription provider using Gemini Files API and structured JSON output.
• Add stable manifest schema v2 with provider-specific metadata envelope.
• Add OpenAI diarized transcription response support.
• Improve Qwen file transcription documentation and provider metadata handling.
• Make sherpa-onnx opt-in by default so clean CI/default builds do not require external ONNX shared libraries.
• Bump product version to 1.4.0.

Validation

• ./scripts/check.sh
• cargo clippy --all-targets -- -D warnings