dsh-usage-cost: Lightweight API Cost Statistics Plugin for DeepSeek Harness

`dsh-usage-cost` is a lightweight plugin for DeepSeek Harness developed by fflow2023, used to calculate API costs. It follows the "everything is a plugin" philosophy, providing read-only cost estimates by replaying persistent session logs. It does not inject any content into the model, ensuring zero impact on token consumption and KV Cache. The plugin supports displaying the current session cost at the bottom of the session and shows a statistics list of global cumulative totals, peak/off-peak splits, and breakdowns by model (V4 Pro/Flash) and session in the settings page. Billing is based on peak/off-peak prices effective on 2026-08-17, with unpriced models counted in `unpricedTokens`. Its implementation is pure JavaScript with zero build steps and zero runtime dependencies, and the Host side event handling complexity is O(1). Users can access it via GitHu...