dsh-context-compression-improved: Context Compression and Code Skeleton Compression Plugin for DeepSeek Harness

The `dsh-context-compression-improved` plugin in DeepSeek Harness addresses context bloat in agent tasks through mechanisms such as pre-compression, aggregate replacement, and history compaction. Its core new feature, the Code Skeleton Gate, substantially reduces oversized source-code tool results by retaining only declarations and key lines, significantly improving inference efficiency. The plugin supports multiple strategies, including Fresh and Aggregate, is compatible only with DeepSeek models, and requires manual enabling of code skeleton compression in the settings.