Add Branched Editing and Timeline to DeepSeek Harness Sessions with dsh-message-edit

`dsh-message-edit` is a DeepSeek Harness session and message plugin maintained by Moeblack. It uses event sourcing to enable branch-style message editing: it allows modifying finalized user texts, thought blocks and replies, and supports regeneration, arbitrary round retries and version timelines. Each operation creates a new session branch before the target round, while the original session is retained and can be switched back to; it does not rewrite history or roll back workspace files. The current npm version is 0.2.3, which requires a web profile. The directory page installation command is `dsh plugin add github:Moeblack/dsh-message-edit`.