dsh-autogate: DSH Auto-Approval Plugin

dsh-autogate is an auto-approval plugin for DeepSeek Harness designed to reduce manual approval in DSH Auto sessions while maintaining the `workspace-write` sandbox boundary. It employs a layered decision mechanism: the L0 layer determines routine operations, such as read-only access and workspace editing, using deterministic rules with zero cost; the L1 layer utilizes a Large Language Model (LLM) to perform safe approval for semantically dangerous operations; and the L2 layer provides a human fallback, where the semi-automatic mode (auto-ask) retains human pop-ups, while the fully automatic mode (auto) relies on the LLM's ruling as the final decision. The plugin adopts a fail-closed strategy, defaulting to rejection in case of exceptions or timeouts. It defends against prompt injection via input masking and label isolation, though these are soft measures and cannot completely eliminate risk. Approval trajectories are only retained within the process memory.