dsh-catalog-refresh: Rebuilding the Model Catalog in DSH

The `dsh-catalog-refresh` plugin is designed for DSH to address the lag in updating static model lists by fetching model lists in real time from APIs and patching the registry of the `@earendil-works/pi-ai` package. It supports multiple providers, including OpenRouter and Fireworks, and provides automatic refresh, caching, and inference effort level configuration. The plugin triggers real-time updates in the model selector by writing to the header, without requiring a restart. Install it using the `dsh plugin add` command, and control its behavior via environment variables such as `CATALOG_REFRESH_INTERVAL_HOURS`.