[mcp] Support server-driven elicitations (#17043)

- [x] Enables MCP elicitation for custom servers, not just Codex Apps
- [x] Adds an RMCP service wrapper to preserve elicitation _meta
- [x] Round-trips response _meta for persist/approval choices
- [x] Updates TUI empty-schema elicitations into message-only approval
prompts

codex-rs/rmcp-client/src/lib.rs

@@ -1,4 +1,5 @@
 mod auth_status;
+mod elicitation_client_service;
 mod logging_client_handler;
 mod oauth;
 mod perform_oauth_login;