Expand WebSocket voice-turn coverage for api/ws/voice.py #51

Summary

Coverage ratchet calls out api/ws/voice.py as a high-gap module. Existing WS tests lean on session lifecycle; audio-turn e2e exists for listening but coverage docs still want this path expanded toward the 75% ratchet.

Context

• docs/testing/coverage.md (high-gap list + 75% ratchet)
• src/voxforge/api/ws/voice.py
• tests/integration/test_websocket_audio_turn_e2e.py
• tests/integration/test_voice_pipeline_e2e.py
• docs/architecture/ci-hardening.md

Acceptance criteria

• Additional mock-provider WS turn assertions (messages + eval artifacts)
• Measurable coverage increase on api/ws/voice.py (report in PR)
• No live STT/LLM/TTS keys
• Distinct from Browser test for microphone-triggered barge-in #31 (Playwright barge-in)

Keep tests hermetic for PR CI.