dsh-session-manager: Session Management Plugin for DeepSeek Harness

dsh-session-manager is a session management plugin for DeepSeek Harness (DSH), designed to provide developers with a unified entry point for maintaining local sessions. This plugin is compatible with DSH version 0.1.0-rc.8, allowing centralized session management within `dsh web` without modifying the core source code. Its main functionalities include: listing all materialized sessions on the local machine (running, idle, archived); continuing existing sessions via a browser; viewing session outlines and statistics based on recent windows; and permanently deleting sessions, with support for cascading deletion of sub-sessions and batch operations. In terms of security, the plugin enforces strict security checks. The delete function is only accessible under loopback addresses, while non-local access is limited to continuing sessions and viewing outlines. It supports both JSONL and SQLite storage formats.