dsh-plugin-anti-rot: DeepSeek Harness plugin for compressing tool error payloads

The DeepSeek Harness (DSH) plugin mitigates “context rot” in long sessions by compressing verbose tool error stack traces. In the `tools/post-execute` phase, it identifies failure signals (`isError` or a non-zero exit code), truncates error text to a specified number of lines and removes indented stack lines, while preserving a truncation marker. After installation, it must be enabled in the configuration file with a positive integer `maxLines` parameter. The tool effectively reduces noise and saves context budget, leaving successful calls unchanged.