dsh-model-balance: Display account balance and quota before the DSH Web GUI model selector

dsh-model-balance is a plugin designed specifically for the DSH Web GUI, aiming to address the pain point of frequently switching consoles to check balances during the development of multiple model providers. This plugin does not alter the model invocation chain; instead, it displays the real-time balance or quota of supported API vendors—such as DeepSeek, StepFun, Kimi, OpenRouter, MiniMax, and xAI—directly before the model selector. For vendors without an API interface, such as Tongyi and Xiaomi, it provides a link to their console. The plugin features an intelligent refresh mechanism, including instant display when switching models, forced refresh after a conversation ends, timed polling every two minutes, and manual refresh on click. It also utilizes distinct caching strategies for success and failure results to ensure state accuracy. Users can easily install it using the npx command from GitHub or npm.