dsh-compact: DeepSeek Harness Context Compression and Overflow Recovery Plugin

`dsh-compact` is a context management plugin for DeepSeek Harness, designed to address context overflow caused by long conversations or frequent tool calls. It automatically compresses historical messages, provides manual compression controls, and includes an overflow recovery mechanism: when context usage reaches 75%, it automatically generates summaries to replace older content, and it attempts retries when an overflow error occurs. The plugin supports basic mounting and Agent-level mounting, offering flexible configuration strategies to effectively maintain coherence in long conversations.