Remote browser tabs should resolve localhost to the remote host or support port forwarding

Problem

When Codex is connected to a remote Mac, the in-app browser tab is opened from the client host. If a service is running on the remote Mac at 127.0.0.1:<port>, navigating the browser tab to http://localhost:<port> resolves localhost on the client host instead of the remote Mac. This makes it difficult to inspect or use development servers and other local-only services on the remote machine.

Reproduction

1. Connect Codex Desktop on client Mac A to remote Mac B.
2. On Mac B, start a service bound to 127.0.0.1:3000.
3. Open the Codex in-app browser from the client connection.
4. Navigate to http://localhost:3000.

The browser either reaches a client-host service or fails to connect; it does not reach the service on Mac B.

Expected behavior

When the active Codex context is a remote connection, users should have one of these supported paths:

• localhost in the browser tab is proxied to the remote host, so http://localhost:3000 reaches Mac B; or
• Codex provides an explicit port-forwarding control, for example remote 3000 -> client 3000, with clear lifecycle, port-collision handling, and security confirmation.

The UI should make it clear whether a browser tab is local or remote and which host a forwarded port targets. A per-tab or per-connection mapping would also allow multiple remote sessions without ambiguous localhost behavior.

Related

Related to #26170, which covers SSH LocalForward handling but not browser access to remote localhost services.