Restore archived chats access from the main Codex UI

Summary

Archived chats need to be accessible from the main Codex UI, not hidden under Settings → Archived chats.

This appears to be a regression/removal: a user reports this was available from the main UI roughly two weeks ago, and now there is no obvious way to browse all archived chats from the main sidebar. If the user does not remember the chat name/title, search is not enough.

Current behavior

• Archived chats are effectively hidden in Settings → Archived chats.
• The main sidebar does not provide an obvious Archived view/section.
• Accidental archive feels like the chat disappeared.
• Recovery is not discoverable unless the user already knows the settings location.

Expected behavior

Please restore/add archived chat access to the main UI:

• Add an Archived section/view in the main sidebar.
• Add a command-palette action such as Show archived chats.
• Make search clearly include archived chats or provide an obvious archived filter/badge.
• Show an Undo archive toast immediately after archiving.
• Keep Unarchive available from the thread menu inside the archived-chat list.

Why this matters

Archive is a normal chat-management action, but recovery is currently too hidden. Users who accidentally archive a chat and do not know its title need a direct way to browse archived chats from the primary navigation.

Environment: Codex Desktop on macOS.