Artifact comment threads now recognize pages that manage their own threads

What

• Artifact auto-react logic now checks for pageOwnsThreads: when a thread reports this, auto-react is declined with a "blocked" reason, and a new telemetry event (page_owns_threads, or page_owns_threads_notice_suppressed if the notice can't be shown) is emitted instead of treating it as a normal deactivation.
• A new terminal reason, page_owns_threads, produces messages like "reply not posted (the page keeps its own comment threads)" and "not resolved (the page keeps its own comment threads)," instead of falling through to the generic "needs thread activation" message.
• The tool results for posting a reply or resolving a thread now special-case page_owns_threads === true, telling the model that the target page manages its own comment threads and that replying or resolving through the session's relay tool is a no-op it shouldn't retry.

Why Some artifact pages handle their own comments outside of Claude Code's relay. This change stops Claude from repeatedly trying (and failing) to react to, reply to, or resolve threads on those pages, and gives a clear explanation instead.