dsh-auto-git: Automatic git init for every newly registered DSH workspace

`dsh-auto-git` is a host-side plugin for DSH workflows that addresses the issue of git-related features being unavailable when a directory has not been initialized. By listening for workspace registration events, it automatically runs `git init`, creates an initial commit for new workspaces, and supports configurable branch names and idempotent handling. The plugin has zero runtime dependencies, and a restart of `dsh web` is required after installation for it to take effect.