Preserve request_user_input option picker metadata

[rafael-jac]

Summary

• add optional inputType and optionPickerAllowMultiple metadata to request_user_input
• preserve that metadata through the core session event and app-server request bridge
• expose the new tool schema fields while keeping existing structured input behavior unchanged

Verification

• cargo check -p codex-app-server -p codex-tools -p codex-protocol -p codex-tui -p codex-app-server-client
• cargo test -p codex-tools request_user_input
• manually launched Electron onboarding flow against a freshly built local CLI via CODEX_CLI_PATH and verified the option-picker path rendered successfully

[rafael-jac]

Superseded by the split stack:\n\n- Plumbing: https://github.com/openai/codex/pull/23818\n- Gated onboarding tools: #23819