[UX] Ask for confirmation before archiving a session — easy to archive by mistake from the context menu

Summary

Archiving a session from the sidebar's right-click context menu happens immediately, with no confirmation and no undo affordance. Because "Archive" sits in a context menu that's easy to open unintentionally (and adjacent to other items), it's quite easy to archive a session by mistake with a single misclick.

This is compounded by the fact that archiving is currently a one-way door in practice: there is no Archived view in the desktop sidebar and no programmatic unarchive path (see #67835), so an accidental archive can feel equivalent to losing the session.

Steps to reproduce

1. In the Claude Desktop app (macOS), right-click a session in the sidebar.
2. Click "Archive" — intentionally or not.
3. The session disappears immediately. No confirmation dialog, no undo toast, and no obvious way to get it back.

Suggested fix

Either (or both) of the standard patterns would solve this:

• Confirmation dialog before archiving ("Archive this session?"), ideally with a "don't ask again" option for users who archive frequently, or
• Undo toast after archiving ("Session archived — Undo"), which keeps the action one-click for intentional use while making mistakes recoverable.

Related issues

• #67835 — Session archive is one-way: no unarchive tool and no Archived view in desktop. The lack of a discoverable undo path is what makes accidental archiving painful; a confirmation/undo affordance would mitigate it even before unarchiving ships.
• #69457 — X button on home screen session cards archives the session. Different trigger surface (session cards vs. context menu), same underlying problem: archive is too easy to hit by accident for an action with no visible recovery path.

Environment

• Claude Desktop app, macOS (Darwin 25.5.0)