DeepSeek Harness Aggregated Web Search Plugin

The `dsh-web-search-aggregation` plugin unifies multiple search providers—including AnySearch, TinyFish, and Tavily—into a single entry point. It enhances availability through a priority queue and an ordered fallback mechanism, supporting multi-key pool rotation, budget-aware timeouts, and real-time configuration. This plugin addresses the issue of a single search service becoming unavailable and is well suited for high-availability web search scenarios involving DeepSeek Harness agents.