dsh-token-pricing: Add per-model token pricing and cost viewing to the DSH Web interface

dsh-token-pricing is a community third-party plugin for the dsh Web interface designed to address token unit pricing discrepancies across different models and peak-hour billing issues. It allows users to configure USD prices for input, output, and cache hits by provider and model, and supports multi-tier pricing for peak hours. Core features include displaying real-time costs at the bottom of the session, offering a draggable floating window (supporting per-turn or per-model views), a cross-project cost statistics panel, and CSV export. Upon modifying price rules, the system automatically recalculates historical session costs. The plugin is easy to install, requires Node ≥22, and can be added to the Web configuration via the `dsh plugin` command. Its design ensures zero token impact by adding no tools or prompt segments to model requests, thereby preserving original interactions. Although a non-official plugin, it relies on lightweight...