dsh-providers: Manage model providers, login, and usage for DeepSeek Harness

`dsh-providers` is a model provider plugin for DeepSeek Harness (DSH), designed to centrally manage model login, directory refresh, usage monitoring, and quota viewing. The plugin supports OAuth or API Key login, allows switching between multiple accounts under the same provider, and enables refreshing the model list from the Curated Catalog or OpenAI-compatible endpoints. In terms of cost management, it provides multi-dimensional views of token consumption and estimated costs for today, 7/30/90 days, supports breakdown statistics by model and provider, and allows manual input of prices for unpriced models for real-time recalculation. Additionally, the plugin can display subscription quotas or pay-as-you-go balances, as well as detailed session-level statistics including tokens, costs, tool calls, cache hit rates, and context peaks. Regarding data security,