fno2010/dsh-web-search-ext: Multi-backend web_search and web_fetch extensions for DSH

fno2010/dsh-web-search-ext is a network extension plugin designed for DeepSeek Harness (DSH) to address issues related to single backend dependency and mandatory API key configuration. It integrates dual backends—Exa and Firecrawl—supporting the use of web_search and web_fetch functions without an API key, while also allowing the configuration of a key to increase quotas. Its core strengths include automatic failover, which automatically switches backends upon encountering 429, 5xx, or network errors, along with a cooling mechanism. Additionally, it features result liveness checks (L0/L1) and source tracing capabilities, displaying the actual backend, latency, and rate limit details. The plugin is written in pure ESM JavaScript and requires no build step.