feat(session): add archive undo + unarchive command

[anduimagui]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds a proper unarchive flow and makes archive easy to undo.

What changed:

• Added desktop menu items for:
  • Archive Session (Cmd+Shift+Backspace)
  • Unarchive Session (Cmd+Shift+U)
• Added session.unarchive in the app command registry.
• Added an archive success toast with an Undo action.
• Fixed the ordering issue on restore: unarchived sessions now go back to their previous spot instead of jumping to the top.
• Updated backend + SDK types so archived can be cleared (null) and unarchive can preserve the old updated timestamp.

Why this solves it:

• Archive is now reversible from both keyboard/menu and the toast.
• Restoring a session keeps list ordering stable, so UX feels consistent.

How did you verify your code works?

• bun install
• ./packages/sdk/js/script/build.ts
• bun run typecheck in:
  • packages/app
  • packages/desktop
  • packages/opencode
• Push hook also ran bun turbo typecheck successfully.

Screenshots / recordings

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on the search results, here are potentially related PRs (excluding the current PR #16212):

Related PRs:

1. feat(session): add lifecycle management — storage reclamation, CLI commands, VACUUM support #16201 - feat(session): add lifecycle management — storage reclamation, CLI commands, VACUUM support

   • Likely related to session archive/unarchive functionality

2. fix: unarchive session on touch, stop cache eviction on archive #16031 - fix: unarchive session on touch, stop cache eviction on archive

   • Directly related to unarchive behavior and archive handling

3. feat(app): unarchive sessions #16001 - feat(app): unarchive sessions

   • Similar feature for unarchiving sessions in the app

4. feat(app): view archived sessions & unarchive #15250 - feat(app): view archived sessions & unarchive

   • Related feature for viewing and unarchiving archived sessions

5. feat: add session archive/unarchive support to TUI #13961 - feat: add session archive/unarchive support to TUI

   • Related archive/unarchive implementation for TUI

6. Feat/view archived sessions #6769 - Feat/view archived sessions

   • Earlier related work on archived session viewing

Note: The most recent and relevant duplicates appear to be #16031, #16001, and #15250, which all involve unarchive functionality. You may want to review these to ensure the work doesn't overlap or cause conflicts.

[anduimagui]

This builds on the same unarchive groundwork from related PRs, but the main UX goal here is speed to immediately undo if it was a mistake. like Gmail’s “Undo Send” toast, instead of having to navigate elsewhere to restore a session.