fix: accept responses path appended to chat completions base

[lawyer112]

Summary

• Accept /v1/chat/completions/v1/responses as a compatibility path for clients that append the Responses endpoint to a Chat Completions base URL.
• Accept /v1/chat/completions/v1/responses/compact with the same compatibility behavior.
• Add a regression test that verifies the appended Responses path is routed through the OpenAI Responses handler instead of returning 404 endpoint not supported.

Why

Some clients/configurations can accidentally use http://host:port/v1/chat/completions as the base URL and then append /v1/responses, producing:

/v1/chat/completions/v1/responses

In local reproduction, /v1/responses worked while this appended path consistently returned 404. This compatibility route avoids failing those requests and keeps them within the Responses handling path.

Related: #908

Testing

go test ./... -count=1
ok github.com/router-for-me/CLIProxyAPI/v7/cockpit-cliproxy 0.670s