Add turn_id to Codex skill invocation analytics

[edwardysun3]

Summary

• add turn_id to the Codex skill invocation analytics payload
• populate it from the existing turn-level TrackEventsContext
• update the reducer test expectation so serialized skill_invocation events include the turn id

Why

chatgpt_skill_resource_invocation / fact_skill_product_events already have backend/schema support for turn_id, but Codex skill invocation events were only sending thread_id. This caused Codex Desktop skill invocation rows to keep turn_id null and prevented reliable turn-level joins with artifact/file events.

Validation

• cargo test -p codex-analytics reducer_ingests_skill_invoked_fact

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[edwardysun3]

I have read the CLA Document and I hereby sign the CLA