fix: forward originator to Codex Apps MCP

[raquel-openai]

Summary

• Forward Codexs canonical originator header on ChatGPT-hosted Apps and plugin-runtime MCP requests.
• Preserve the configured X-OpenAI-Product-Sku header.
• Cover originator-only and originator-plus-SKU configurations.

Why

Sites project creation is logged downstream of Apps MCP. Production validation found CODEX_UNKNOWN_DEFAULT project-created threads that matched codex_surface=desktop_app and originator=Codex Desktop in fact_codex_cli (query).

The hosted Apps MCP configuration forwarded the product SKU but not Codexs canonical originator, so codex-backend could not derive CODEX_DESKTOP_APP for those tool calls.

Validation

• just fmt
• CARGO_HOME=/private/tmp/codex-cargo-home CARGO_TARGET_DIR=/private/tmp/codex-target just test -p codex-mcp (106 passed)
• CARGO_HOME=/private/tmp/codex-cargo-home CARGO_TARGET_DIR=/private/tmp/codex-target just fix -p codex-mcp

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[raquel-openai]

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