dsh-concurrency-guard: Concurrent Request Monitoring and Latching

`dsh-concurrency-guard` is a concurrency monitoring and throttling plugin for DSH. By hooking into DSH's model request bus, it provides complete statistics and FIFO queuing, effectively preventing risk-control bans caused by exceeding concurrency limits. The plugin supports session-level control, a real-time monitoring dashboard, and HTTP interface configuration, making it suitable for complex workflows that require strict management of API concurrency quotas.