DeepSeek Harness Literature Search Plugin

The DeepSeek Harness (DSH) plugin `dsh-literature-search` is designed to address the lack of unified interfaces across multiple literature databases. It supports searching through PubMed and Google Scholar and normalizes the results into a standard `paper` data structure. Its features include PubMed search, single-paper details, related articles, as well as Google Scholar search and citation generation. A DSH restart is required after installation. For use, it is recommended to configure `NCBI_API_KEY` and SerpApi credentials to improve rate limits and stability.