Response transformation crashed with TypeError when counting tokens for
multimodal (dict-shaped) embedding inputs, since encoding.encode() was
called directly on the dict instead of its text parts. Also removed a
dead, equally-buggy duplicate of the same loop in _transform_response.
Separately, the embeddings guardrail handler silently skipped multimodal
dict inputs instead of scanning them, letting prohibited text/image
content bypass the configured guardrail. It now extracts and scans the
text parts while leaving image parts untouched.
