dsh-plugin-edit-regenerate: Edit History Messages and Regenerate

`dsh-plugin-edit-regenerate` is a DeepSeek Harness (DSH) plugin designed to allow users to directly edit user messages in the conversation history and regenerate the response. The plugin provides an editing entry point in the UI; after confirmation, the system forks a new session and regenerates the response from the revised text. It supports fork strategies for both the first message and non-first messages, and retains the copy function. A DSH restart is required after installation for it to take effect. When using it, note that attachments will be lost after revision; forked sessions may fail to load after a restart because they are stored as append-only logs (a repair script must be run); and dependencies must be manually refreshed after updating the source code.