Populate workspace kind on Codex turn events

[knittel-openai]

Summary

• carry workspace_kind from Responses API client metadata into the turn resolved analytics fact
• serialize the optional value on codex_turn_event
• cover both the turn metadata source and turn event serialization

The workspace_kind tells us whether a thread had a project attached vs projectless. this is an indicator for who is adopting Codex for knowledge work outside of coding

Testing

• env UV_CACHE_DIR=/private/tmp/uv-cache /private/tmp/cargo-tools/bin/just fmt
• env PATH=/private/tmp/cargo-tools/bin:$PATH CARGO_HOME=/private/tmp/cargo-home UV_CACHE_DIR=/private/tmp/uv-cache /private/tmp/cargo-tools/bin/just test -p codex-analytics
• env PATH=/private/tmp/cargo-tools/bin:$PATH CARGO_HOME=/private/tmp/cargo-home UV_CACHE_DIR=/private/tmp/uv-cache /private/tmp/cargo-tools/bin/just test -p codex-core turn_metadata

Paired with openai/openai#970661, which keeps forwarding the same metadata key through Responses API headers.

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[knittel-openai]

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