fix(llm): forward base_url via api_base for litellm.completion; keep responses using api_base already

- Align litellm completion kwargs to use api_base (some providers expect this)

Co-authored-by: openhands <openhands@all-hands.dev>

Author: enyst

openhands-sdk/openhands/sdk/llm/llm.py

@@ -668,7 +668,7 @@ def _transport_call(
                 ret = litellm_completion(
                     model=self.model,
                     api_key=self.api_key.get_secret_value() if self.api_key else None,
-                    base_url=self.base_url,
+                    api_base=self.base_url,
                     api_version=self.api_version,
                     timeout=self.timeout,
                     drop_params=self.drop_params,