perf(client): stop thread streams when unused (#9740)

Close a thread's live detail stream when its last consumer leaves. Retain a registry-local completed state and replay cursor for five idle minutes.

Keep warm lookup independent of collectible raw atom definitions. Preserve paging and deletion state, reject stale owners, and cache only completed data/cursor updates.

Skip repeated saves of unchanged data while retaining dirty-data flushes and failed-write retries. Verify real GC/remount behavior and focused lifecycle cases.

Created with GPT-6 Astra (preview) in Codex.