Fix Dockerfile: use pip instead of uv sync --frozen

uv sync --frozen failed on HF base image due to Python version mismatch.
Switching to pip install for reliable cross-version dependency install.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -3,9 +3,8 @@ FROM ghcr.io/meta-pytorch/openenv-base:latest
 WORKDIR /app
 COPY . .
 
-RUN uv sync --frozen
+RUN pip install --no-cache-dir openenv-core fastapi "uvicorn[standard]" pydantic && pip install --no-cache-dir -e . --no-deps
 
 EXPOSE 8000
 
-CMD ["uv", "run", "uvicorn", "server.app:app", \
-     "--host", "0.0.0.0", "--port", "8000"]
+CMD ["python", "-m", "uvicorn", "server.app:app", "--host", "0.0.0.0", "--port", "8000"]