Improve Codex Desktop support for SSH remote workspaces

Summary

I would like Codex Desktop to support SSH-based remote workspaces as a first-class workflow.

This is specifically about the Codex Desktop app, not about manually SSH-ing into a server and running Codex CLI there.

Concrete environment

• Local client: Codex Desktop on macOS
• Remote host: Linux server over SSH
• Code location: on the Linux remote host
• Desired workflow: use the macOS Codex Desktop app as the UI/client, connect to the Linux SSH host, choose a remote repository directory, and have Codex operate entirely in that remote workspace.

In this setup, the local Mac should mostly be the Desktop UI. The actual filesystem, shell commands, tests, services, and development dependencies should come from the Linux SSH host.

Desired Desktop workflow

• Codex Desktop can add, connect to, and manage SSH hosts directly.
• After connecting, Codex Desktop uses the remote host's filesystem and shell as the active workspace environment.
• Users can choose a remote directory as the workspace from within Codex Desktop.
• Codex Desktop can read and edit remote files, run commands, run tests, and start services on the remote machine.
• Codex Desktop provides a clear remote environment initialization flow, including checking whether required components are installed on the remote host.
• When SSH connection, authentication, permissions, remote shell configuration, bootstrap, or PATH setup fails, Codex Desktop gives clear diagnostic messages.
• Users should not need to manually open an SSH terminal and run Codex CLI on the remote host to get this workflow.

Relation to existing issue

This is related to #10450, but this issue is intended to emphasize the Desktop-specific product experience now that remote connections exist but still feel incomplete for production remote-development workflows.

The main ask is not just generic remote development support. It is for Codex Desktop to own the SSH remote workspace flow end to end: host management, remote directory selection, remote filesystem/shell execution, environment bootstrap, and clear diagnostics.

If this issue is considered a duplicate of #10450, I hope these Desktop-specific requirements and the macOS-to-Linux remote workflow can be folded into that tracking issue.