feat(codex): forward native Responses with Codex upstream constraints

[caigee-cmd]

Summary

• Keep /v1/responses on the original request and route it only to adapters that implement native Responses, instead of rebuilding it through ChatRequest.
• Apply the ChatGPT Codex request constraints used by CLIProxyAPI (forced stream/store/include, rejected sampling fields, item id normalization, tool schema cleanup, routing and responses-lite headers) to both the native path and Chat/Messages requests translated into Codex Responses.
• Collect a complete non-stream Responses object from the upstream SSE terminal event, restore namespace tool names, and treat response.failed as a terminal error without appending a second error frame.

Test plan

• go test ./internal/providers/codex ./internal/translate ./internal/executor ./internal/gateway
• Live ChatGPT Codex account acceptance for /v1/responses, /v1/chat/completions, and /v1/messages