dsh-code-lens: Observing Subcalls in DeepSeek Harness Code Mode

`dsh-code-lens` is an observability plugin for DeepSeek Harness code mode, designed to address the gap where models cannot perceive tool calls triggered by internal programs. It provides two core features: first, it generates session-level aggregate data via the `codeLens` view, displaying statistics such as `hiddenBytes` (bytes consumed but not included in the model context); second, it provides the `code_lens` tool, enabling post-hoc auditing of specific subcall details. The plugin supports Headless mode, is zero-dependency, and can display non-settled subcall chains. Developers can install it via `dsh plugin` to monitor internal program calls, analyze hidden data, and audit subcall chains.