feat(ai): add Hugging Face provider support

- Add huggingface to KnownProvider type
- Add HF_TOKEN env var mapping
- Process huggingface models from models.dev (14 models)
- Use openai-completions API with compat settings
- Add tests for all provider test suites
- Update documentation

fixes #994

packages/ai/test/cross-provider-handoff.test.ts

@@ -86,6 +86,8 @@ const PROVIDER_MODEL_PAIRS: ProviderModelPair[] = [
 	{ provider: "cerebras", model: "zai-glm-4.7", label: "cerebras-zai-glm-4.7" },
 	// Groq
 	{ provider: "groq", model: "openai/gpt-oss-120b", label: "groq-gpt-oss-120b" },
+	// Hugging Face
+	{ provider: "huggingface", model: "moonshotai/Kimi-K2.5", label: "huggingface-kimi-k2.5" },
 	// Mistral
 	{ provider: "mistral", model: "devstral-medium-latest", label: "mistral-devstral-medium" },
 	// MiniMax