DeriveUpstreamEndpoint maps every OpenAI-platform request to /v1/responses, but
API-key accounts whose upstream only speaks Chat Completions
(!ShouldUseResponsesAPI) are forwarded directly to /v1/chat/completions. The
messages, responses and cyber-policy recording sites derived the endpoint via the
bare GetUpstreamEndpoint, so usage/ops records mislabeled those requests as
/v1/responses. Generalize the existing resolveRawCCUpstreamEndpoint into
resolveOpenAIUpstreamEndpoint and use it at every OpenAI recording site, matching
the already-correct chat-completions client path.