Read hf_soci_token env var for HF Inference API key

Adds hf_soci_token to the fallback chain so the HF Space secret
created under that name is picked up automatically.
Lookup order: HF_TOKEN → hf_soci_token → soci_token

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/soci/engine/llm.py

@@ -825,7 +825,7 @@ class HFInferenceClient:
         default_model: str = MODEL_HF_ZEPHYR,
         max_retries: int = 3,
     ) -> None:
-        self.api_key = api_key or os.environ.get("HF_TOKEN", "") or os.environ.get("soci_token", "")
+        self.api_key = api_key or os.environ.get("HF_TOKEN", "") or os.environ.get("hf_soci_token", "") or os.environ.get("soci_token", "")
         if not self.api_key:
             logger.warning(
                 "Neither HF_TOKEN nor soci_token is set — HF Inference will not make LLM calls. "