Add APIFree as a built-in OpenAI-compatible provider. APIFree offers
agent-optimised models such as skywork-ai/skyclaw-v1 through an
OpenAI-compatible API at https://api.apifree.ai/agent/v1.
Changes:
- Register apifree provider in the provider registry
- Add config schema field
- Add documentation with configuration example
- Add provider tests, websocket channel tests, and webui tests
- Add provider icon in settings UI
