Dictation/transcription requests return 403 with Node’s default user-agent

[domsj]

On Codex Desktop 26.901.41123, recording works in codex-web, but speech-to-text fails because POST /backend-api/transcribe returns a Cloudflare 403.

I traced this to the Electron net.fetch shim using Node’s default user-agent. With the same authentication and request:

• Node/Undici’s default user-agent returns 403.
• Codex Desktop/26.901.41123 (X11; Linux; x64) reaches the API and returns the expected validation response.
• Supplying the Codex Desktop user-agent in the shim fixes dictation locally. It also appears relevant to other authenticated desktop requests that were returning 403.

Proposed fix: domsj@8cc7c4b

If this approach looks good, I’m happy to open a PR.