Add Dockerfile for GPU support (MinerU, Marker)

[kiyeonjeon21]

What

Current Dockerfile is CPU-only. Add a GPU variant for MinerU and Marker.

How

1. Create `Dockerfile.gpu` based on NVIDIA CUDA base image
2. Install all parsers including MinerU and Marker
3. Update `docker-compose.yml` with GPU profile
4. Test on a machine with NVIDIA GPU

Files

• `Dockerfile.gpu` (new)
• `docker-compose.yml` — add GPU service profile