feat: extract several selected archives at once (one folder per archive) #69

Summary

Mark multiple archives and extract them in one action, each into its own dedicated folder (spec default).

Motivation

Batch extraction is common after downloads.

Requirements

• Never mixes contents; queued as separate operations with individual results.

Controller UX

Mark archives → North → Extract each to its own folder.

Technical Notes

Enqueue one extraction per archive via the existing flow.

Acceptance Criteria

• Three marked archives produce three dedicated folders with their own results.

Testing

Unit tests for new branches and for every bug reproduced before a fix (no trivial variations, see AGENTS.md).

Dependencies

• None

Priority: medium · Milestone: 6 · Archives