DeepSeek Harness Plugin: Retry, Edit Prompt, and Continue Actions for Chat Turns

The `locietta/dsh-rewind-retry` plugin adds Retry, Edit prompt, and Continue actions to DeepSeek Harness (DSH). At its core, it works by forking a conversation: Retry and Edit fork at turn boundaries to resubmit or modify the prompt, while Continue simply continues in the current conversation. The plugin can be installed directly from GitHub; it supports only manually initiated turns, and Retry is limited to text, requiring attachments to be added manually.