feat: add --idle-timeout CLI flag for daemon auto-shutdown (#856)

* feat: add --idle-timeout CLI flag for daemon auto-shutdown

Add user-friendly --idle-timeout flag that converts time strings
to milliseconds. Supports formats like '10s', '3m', '1h', or raw ms.

This addresses a common need for ephemeral/CI environments where
daemon processes can be orphaned if not explicitly closed, leading
to resource consumption from zombie chrome-headless-shell processes.

Co-authored-by: Hermes (via claude-sonnet-4-20250520) <agent@hermes.ai>

* fix: address idle-timeout review feedback

* fix: normalize idle-timeout parsing

---------

Co-authored-by: Merlin <merlin@rbeckner.com>
Co-authored-by: Hermes (via claude-sonnet-4-20250520) <agent@hermes.ai>

cli/src/main.rs

@@ -316,6 +316,7 @@ fn main() {
         action_policy: flags.action_policy.as_deref(),
         confirm_actions: flags.confirm_actions.as_deref(),
         engine: flags.engine.as_deref(),
+        idle_timeout: flags.idle_timeout.as_deref(),
     };
     let daemon_result = match ensure_daemon(&flags.session, &daemon_opts) {
         Ok(result) => result,