Feature request: session unarchive — archived sessions currently have no way back

[qtxxgedfs]

The session context menu offers Archive session, but there is no unarchive: an archived session disappears from every grouping surface and from search, with no restore path anywhere in the GUI. Archiving is explicitly non-destructive (the session log and the workspace sessionIds accounting slot are kept, and the code comments say "a future unarchive restores its position"), so this looks like a missing inverse rather than a design choice.

I have prepared a complete implementation (reference PR available on request) that mirrors the archive path end to end:

• WorkspaceRegistry.unarchiveSession(id) — durable set removal, no-op for ids outside the set, accounting untouched
• workspace.unarchiveSession RPC (schema/rpc-map/fetch carrier/handler); the existing domain/changed listener already streams host/archived-sessions-changed for set shrink, so all clients update live
• Client IWorkspaces.unarchiveSession + runtime methods
• Minimal UI: a footer Archived entry under the sidebar session list opens a panel of archived sessions grouped by workspace (newest first), each with a Restore action
• Unit tests at every layer plus a web e2e round-trip

I understand external PRs are not accepted yet (CONTRIBUTING). Happy to submit the PR if that changes, or to reshape this as a community plugin once the host API lands. Would the team consider adding unarchive upstream?