dsh-price-phase: Peak/Off-Peak Phase Badge for DSH Web GUI

The `dsh-price-phase` plugin is designed to help users intuitively understand changes in DeepSeek's billing periods. It displays in real time at the bottom of the DSH Web GUI input card whether the current status is "peak" or "off-peak," with a countdown. The plugin supports hovering to view detailed information, adapts to narrow screens, and accurately handles countdowns spanning weekends. It is installed via a terminal command, has no third-party library dependencies, uses Beijing time as the reference, and does not affect numerical price calculations.