Add VibeVoice-ASR backend

Third ASR backend option alongside faster-whisper and qwen3. Builds
microsoft/VibeVoice from source (pinned to a specific commit, since it's
custom modeling code not in transformers' Auto* registry) into its own venv,
inheriting the base image's torch/CUDA. Comes with built-in speaker
diarization (VibeVoiceASRProcessor.post_process_transcription returns
per-segment speaker ids directly, no separate pyannote pass needed).

Verified end-to-end against a real recording: 200 OK, correct Korean
transcription, speaker labels populated.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Containerfile

@@ -38,6 +38,19 @@ RUN python -m venv --system-site-packages /opt/venvs/xtts && \
     /opt/venvs/xtts/bin/pip install --upgrade pip && \
     /opt/venvs/xtts/bin/pip install -r /build/envs/xtts.txt
 
+# vibevoice는 pip 패키지가 아니라 GitHub 소스를 직접 빌드해야 함(커스텀 모델링 코드,
+# transformers Auto* 레지스트리에 없음). 특정 커밋에 고정해 업스트림 변경에 흔들리지 않게 함.
+RUN apt-get update && apt-get install -y --no-install-recommends git && rm -rf /var/lib/apt/lists/* && \
+    git clone https://github.com/microsoft/VibeVoice.git /opt/vibevoice_src && \
+    cd /opt/vibevoice_src && git checkout 303b2833e01cff4578ec278bbfe536da54bd19fe
+
+# vibevoice venv — base image의 torch/CUDA 상속. fastapi/uvicorn/python-multipart는
+# vibevoice의 pyproject.toml(직접 의존성 또는 gradio 경유 간접 의존성)으로 이미 호환되는
+# 버전이 설치되므로 별도 requirements 파일 불필요.
+RUN python -m venv --system-site-packages /opt/venvs/vibevoice && \
+    /opt/venvs/vibevoice/bin/pip install --upgrade pip && \
+    /opt/venvs/vibevoice/bin/pip install -e /opt/vibevoice_src
+
 COPY app/ /app/
 
 RUN chmod +x /app/start.sh