Add account/workspace switching support

Feature request

Codex currently supports signing out and signing back in, but it does not appear to support quick switching between multiple accounts or workspaces.

Requested behavior

• Show the current signed-in account and workspace clearly in Codex app, CLI, and IDE extension.
• Add a switch account/workspace action.
• Keep separate cached sessions per account/workspace where possible.
• Avoid requiring users to repeatedly log out and log back in.

Use case

Developers often need to switch between personal and company accounts, or between different ChatGPT workspaces/API organizations. Re-authenticating each time is inconvenient and can lead to confusion because permissions, billing, and managed workspace policies may differ by account or workspace.

Current workaround

Run codex logout and then codex login again with the other account.