Dashboard: allow binding to 0.0.0.0 (or add a `--host` flag) so it works from Docker

Right now the dashboard only binds to 127.0.0.1 and [::1] (run_dashboard_server in cli/src/native/stream/dashboard.rs). That makes it annoying to use inside a Docker container. Publishing the port with -p 4848:4848 doesn't help, because Docker forwards traffic to the container's network interface, not its loopback, so localhost:4848 on the host never reaches the dashboard.

What I'd like is to run agent-browser in a container, publish the port, and open http://localhost:4848 on my host. Next.js dev does this by default.

Options:

1. Bind to 0.0.0.0 / :: by default, like next dev.
2. Or keep loopback as the default and add --host <addr> (plus something like AGENT_BROWSER_DASHBOARD_HOST), so I can run agent-browser dashboard start --host 0.0.0.0.

I get why loopback is the safe default, so option 2 is totally fine. Right now the only way around it is a socat or nginx sidecar inside the container, which feels like overkill for a dev tool.

Thanks!