feat(desktop): add bulk archive/unarchive for sessions

[nurazhardotcom]

Summary

Adds bulk archive/unarchive capability for sessions in Hermes Desktop. Users with many sessions can select multiple and archive/unarchive them in one action instead of clicking each session's kebab menu individually.

Changes

Backend:

• POST /api/sessions/bulk-archive endpoint in hermes_cli/web_server.py
• Mirrors the existing bulk-delete pattern with 500-item cap
• Unknown IDs silently skipped (same behavior as bulk-delete)

Frontend:

• archiveSessions() helper in apps/desktop/src/hermes.ts

Tests:

• test_bulk_archive_sessions and test_bulk_unarchive_sessions in tests/hermes_cli/test_web_server.py

Notes

• UI selection checkboxes and bulk action bar in session-row/sidebar components are still needed for the full feature. This PR covers the backend endpoint and frontend API helper.
• All existing tests pass.

Testing

• python -m pytest tests/hermes_cli/test_web_server.py -x -q — all green

[alt-glitch]

Related: #39376 (broader competing implementation) and feature request #48843. This PR covers only the backend /api/sessions/bulk-archive endpoint plus the archiveSessions() frontend API helper (UI selection/bulk-action bar still pending), whereas #39376 includes the full sidebar UI wiring. Reviewers should reconcile the two approaches for #48843.

[alaamohanad169-ship-it]

Acknowledged: noted competing PR(s) #39376, #48843, #39376, #48843. My approach differs and is complementary, not mutually exclusive. Open to consolidating if reviewers prefer one direction.