[mcp] Improve custom MCP elicitation (#15800)

- [x] Support don't ask again for custom MCP tool calls.
- [x] Don't run arc in yolo mode.
- [x] Run arc for custom MCP tools in always allow mode.

codex-rs/cli/src/mcp_cmd.rs

@@ -306,6 +306,7 @@ async fn run_add(config_overrides: &CliConfigOverrides, add_args: AddArgs) -> Re
         disabled_tools: None,
         scopes: None,
         oauth_resource: None,
+        tools: HashMap::new(),
     };
 
     servers.insert(name.clone(), new_entry);