The transformation.py file was using FEATHERLESS_API_KEY (missing _AI_)
while the rest of the codebase (get_llm_provider_logic.py, utils.py)
correctly uses FEATHERLESS_AI_API_KEY. This caused 401 auth errors when
the user set FEATHERLESS_AI_API_KEY as documented.
Now checks FEATHERLESS_AI_API_KEY first (canonical name) with fallback
to FEATHERLESS_API_KEY (legacy compatibility). Same fix applied to
FEATHERLESS_AI_API_BASE.
Refs: #22490