Recreate deleted worktrees from their branch on restore

Archiving a Paseo-owned worktree deletes its directory, so reopening its
agent previously dead-ended even after the workspace record came back —
there was no folder to return to.

Restore now recreates the worktree at its original path from the kept
branch (the branch is never deleted on archive), re-points the same
workspace record, and clears archivedAt — preserving the workspaceId so
the agent stays linked. The directory is recreated before the un-archive
so the reconciler can't re-archive it for a missing directory. A deleted
or already-checked-out branch surfaces a typed failure and leaves the
workspace archived.

Gated behind a worktreeRestore capability flag; older hosts get an
explicit "update your host" state instead of a misleading failure.

packages/app/src/i18n/resources/en.ts

@@ -335,6 +335,7 @@ export const en = {
       cannotReachHost: "Cannot reach {{hostName}}",
       hostStatus: "Host status: {{status}}",
       missing: "Workspace not found",
+      needsHostUpgrade: "Update your host to restore this workspace",
       manageHost: "Manage host",
     },
     hoverCard: {