dsh-time-travel: Reversible rollback and auditing for DSH tool side effects

dsh-time-travel is a reversible time-travel and audit tool designed for the DeepSeek Harness (DSH) plugin system, aiming to address the lack of stable rollback entry points resulting from the side effects of model tool execution (such as file read/write, shell commands, and HTTP requests). By monitoring tool pipeline events, the plugin establishes a "pre-state snapshot -> execution -> compensation" chain for file operations like `fs.write` and `fs.delete`, supporting the reverse restoration of the workspace by round. For operations that are difficult to automatically reverse, such as `bash` and `http.request`, it utilizes a built-in audit rule engine to record dangerous behaviors into JSON Lines logs. The plugin provides the `ctx.timeTravel` API, including `rewindTo` (specifying a rollback to a specific round).