[Feature Request] Web UI: archived sessions cannot be viewed or restored

[HanGe88]

Problem

The session context menu has an "Archive session" action, which hides the session from every sidebar view (workspace groups, flat list, and search results). However, there is NO UI entry point to view archived sessions or restore (unarchive) them. Once archived, a session disappears and cannot be recovered through the UI.

Expected behavior

• A "Show archived" toggle or an "Archived" section in the sidebar that lists archived sessions, and
• A "Restore" (unarchive) action on archived sessions so they reappear at their previous position.

Notes

The backend already supports the data model for this:

• archivedSessionIds is persisted durably in the workspace state (~/.dsh/storages/workspace.json), returned by the workspace.archiveSession API.
• Archived sessions keep their slot in the workspace sessionIds; comments in @deepseek-ai/dsh-workspace state: "an archived session keeps its sessionIds slot so unarchiving restores its position".
• But no unarchive API endpoint and no archived-list UI exist yet, so archiving is effectively one-way hide.

Environment

• DSH version: 0.1.0-rc.6 (web UI, http://127.0.0.1:3080)
• OS: Windows 11

Related code

• dsh-client-ui-workspace - sessionVisible() filters out archived.has(session.id) from all views; WorkspaceBrowser reads archivedSessionIds but renders no archived view.
• dsh-workspace - WorkspaceRegistry.archiveSession() appends to archivedSessionIds; no unarchive method.