[Desktop][macOS] Add a dedicated plain Chat view with conversation history to Codex

What variant of Codex are you using?

Codex desktop app for macOS, version 26.825.51511 (build 7377), Apple Silicon, macOS 26.5.1.

What feature would you like to see?

Please add a dedicated plain Chat page or mode inside the Codex section of the macOS desktop app, similar to the chat experience available from the ChatGPT Work page.

The page should let users:

• start a normal conversational chat without selecting a repository, project, worktree, or coding workflow;
• view and reopen the history of those chat-only conversations;
• clearly distinguish chat-only conversations from Codex coding/agent tasks in the sidebar or history view.

Why is this useful?

Codex is also useful for brainstorming, requirement clarification, technical Q&A, and planning before any repository work begins. Today, these conversations can become mixed into coding tasks or require switching to another page, which fragments context and history.

A first-class chat-only page inside Codex would make it easy to keep lightweight conversations and their history available while preserving the existing task/project workflow for agentic coding work.

The issue names no files, tests, or entry points. Start by locating the macOS Codex section and its conversation-history entry point; the feature is done when users can start, reopen, and distinguish chat-only conversations without selecting a repository or coding workflow.