Codex desktop: add compact/collapsible sidebar for recent threads and fixed nav items

What problem are you seeing?

The Codex desktop sidebar spends a lot of vertical space on the recent thread list and the Show more row. On smaller windows this pushes useful project/thread context down and makes the sidebar feel noisy.

The fixed top-level navigation entries also add to the space pressure (New chat, Search, Plugins, Automations, Codex mobile), but the biggest issue is the recent section: several recent thread rows plus Show more take most of the sidebar height before I get to the work I actually want to switch to.

What would you like Codex to do instead?

Please add a way to reduce sidebar space usage, for example:

• collapse or hide the recent threads section
• limit recent threads to 1-2 rows before Show more
• make Show more part of a compact dropdown/menu instead of a full row
• add a compact icon-only mode for fixed navigation items
• allow hiding low-frequency fixed nav items like Plugins, Automations, and Codex mobile

Why this matters

The current layout makes the sidebar less useful as a project/thread switcher because recent items dominate the available vertical space. This is especially noticeable on laptop-sized windows or when the Codex app is not full screen.

This is not a bug about missing threads or Automations being hidden by a rollout flag. It is a UX request for a more compact/collapsible desktop sidebar, with emphasis on the recent threads + Show more section taking too much room.