fix: name spaces and agents by their herdr workspace name

Space chips and agent cards both fell back to the cwd basename, so
several workspaces in one repo rendered identically ("personal",
"monitors", "personal").

Expose the herdr workspace name as workspace_label and prefer it in
both places. Kept separate from label, which tab chips use and which
must stay pane-scoped.

Skipped when the pane list is unusable so an unreachable SSH remote
does not cost a second timeout per poll.