dsh-gpu: GPU-aware Execution Layer of DeepSeek Harness

`dsh-gpu` is a GPU-aware execution layer plugin for DeepSeek Harness (DSH), designed to address the scattered nature of manually concatenating Shell commands and querying states when intelligent agents execute GPU tasks. The plugin provides three core tools: `gpu_status` for querying memory, utilization, and temperature of all GPUs, and determining device busy/idle status based on thresholds; `gpu_exec` for executing one-off commands by automatically setting `CUDA_VISIBLE_DEVICES` to select an idle or specific card; and `gpu_run_bg` for managing long-running background tasks like training and inference, supporting output retrieval or task termination via Job ID. Furthermore, it supports optional per-step context injection and rate-limited GPU snapshots. During installation, ensure...