dsh-cpa: CPA Provider Integration and Agent Routing Plugin

The dsh-cpa plugin aims to integrate CLI Proxy API (CPA) capabilities into DeepSeek Harness (DSH), addressing model routing and multi-model management requirements in agent development. By registering a CPA provider, the plugin supports automatic model list synchronization, intelligent failover, and dual-mode (external/internal CPA) operation. It provides configuration services through an admin panel and consumes only desensitized account data, simplifying the multi-model agent development workflow.