dsh-persist: DeepSeek Harness Long-Term Memory Plugin

The dsh-persist plugin provides hierarchical memory storage for the DeepSeek Harness Agent via the file system, solving the “losing memory when switching conversations” problem. Core features include conversation-specific memory, cross-project sharing, bge-m3-based semantic search, and a three-state automatic recall mode. All memories are stored locally as plain-text Markdown and are human-editable. Users can read and write memories through the `memory` tool or a UI tab. Installation requires Node.js >= 22.6, and enabling semantic search requires a SiliconFlow API key. The plugin’s default data paths and routing remain unchanged, and it supports privacy controls and remote access configuration.