feat(utils): refactored stderr handling API from boolean option to enum-like option

- Changed stderr handling API from `exposeStderr` boolean option to `stderr: "full" | null` enum-like option for clearer intent.
- Refactored ChildProcess constructor to accept stderr parameter directly instead of options object for simpler API.

packages/coding-agent/src/ssh/ssh-executor.ts

@@ -79,7 +79,7 @@ export async function executeSSH(
 	using child = ptree.spawn(["ssh", ...(await buildRemoteCommand(host, resolvedCommand))], {
 		signal: options?.signal,
 		timeout: options?.timeout,
-		exposeStderr: true,
+		stderr: "full",
 	});
 
 	const sink = new OutputSink({