dsh-conversation-guard: Add task identity verification to DSH sessions

dsh-conversation-guard is a DeepSeek Harness community plugin maintained by myboker (MIT, 0.1.0-rc.3). It assesses whether messages belong to the current task before they reach the model; if suspicious, it pauses the entire batch and requests human confirmation. Work from unintended sessions can be exported as Markdown with evidence citations. It supports commands including /guard status, allow, cancel, history, handoff, evidence, and task. Approvals do not grant elevated privileges, and it is compatible only with DSH 0.2.2-alpha.3 / rc.1 and Node.js 24.9+.