[codex] handle request_user_input in app-server test client

[celia-oai]

Why

codex-app-server-test-client previously treated item/tool/requestUserInput as an unsupported server request and terminated the connection. That made it impossible to use the client for end-to-end testing of interactive turns: an operator could observe the request, but could not answer it and confirm that the same turn resumed.

What changed

• Handle ToolRequestUserInput server requests in the test client's central request dispatcher.
• Render numbered terminal choices, accept exact option labels, support free-form Other and text-only questions, and collect multiple answers.
• Send a protocol-native ToolRequestUserInputResponse and continue streaming the active turn.
• Fail clearly when interactive input is requested without a terminal.
• Document the interactive behavior and add focused tests for option selection, free-form answers, multiple questions, and invalid-selection retries.

Testing

• just test -p codex-app-server-test-client
• just bazel-lock-check
• Manually exercised the app-server flow, selected TUI, observed serverRequest/resolved, and verified that the same turn completed with the selected answer.