Rollback Whale: Adding Checkpoint and Recovery CLI for DeepSeek Harness

Rollback Whale is an independent community plugin for DeepSeek Harness (DSH), designed to resolve the issue where the Web profile fails to start after modifying plugins, UI, or control files. It provides a set of checkpoint management tools independent of the current Web profile, allowing users to create immutable checkpoints from the current Git checkout and DSH control files, and perform safe rollbacks when necessary. The plugin's core functions include a management interface in the sidebar and settings, as well as an independent CLI entry (`rollback-whale`), ensuring that recovery operations can still be performed even if the Web interface fails. Checkpoints are stored by default in the `~/.dsh-recovery` directory and are verified via SHA-...