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/connection.rs

@@ -234,6 +234,7 @@ pub struct DaemonOptions<'a> {
     pub action_policy: Option<&'a str>,
     pub confirm_actions: Option<&'a str>,
     pub engine: Option<&'a str>,
+    pub idle_timeout: Option<&'a str>,
 }
 
 fn apply_daemon_env(cmd: &mut Command, session: &str, opts: &DaemonOptions) {
@@ -300,6 +301,9 @@ fn apply_daemon_env(cmd: &mut Command, session: &str, opts: &DaemonOptions) {
     if let Some(engine) = opts.engine {
         cmd.env("AGENT_BROWSER_ENGINE", engine);
     }
+    if let Some(idle) = opts.idle_timeout {
+        cmd.env("AGENT_BROWSER_IDLE_TIMEOUT_MS", idle);
+    }
 }
 
 pub fn ensure_daemon(session: &str, opts: &DaemonOptions) -> Result<DaemonResult, String> {