[app-server] centralize client response analytics

[rhan-oai]

Why

The precursor PR keeps successful client responses typed until app-server's outgoing response seam. This follow-up uses that seam to move successful client-response analytics out of individual handlers and into the shared sender path, while keeping filtering decisions inside codex-analytics.

What changed

• Emit successful client-response analytics centrally from OutgoingMessageSender::send_response.
• Remove duplicate handler-local response tracking for the current thread/turn lifecycle responses.
• Keep analytics ingestion selective inside AnalyticsEventsClient, so unrelated client traffic is ignored before cloning or boxing.
• Collapse client-response analytics facts onto one typed path and normalize payloads in the reducer.
• Add direct client-filter coverage plus sender-level coverage for the centralized forwarding path.

Verification

• cargo test -p codex-analytics
• cargo test -p codex-app-server outgoing_message::tests --lib