## Summary
This PR reduces duplicate failure noise for audio transcription jobs
that fail with permanent HTTP 400 responses, and fixes a file-format
edge case causing intermittent 400s.
Sentry issue: [CHATWOOT-99E /
6660541334](https://chatwoot-p3.sentry.io/issues/6660541334/)
## Confirmed root cause
For some attachments, the stored filename had no extension (example:
`speech`, content type `audio/mpeg`).
When the temporary transcription upload file was created without an
extension, OpenAI returned:
`Unrecognized file format` (HTTP 400).
## Scope of changes
1. `Messages::AudioTranscriptionJob`
- Keeps `discard_on Faraday::BadRequestError` to avoid retry storms on
permanent request errors.
- Adds explicit Rails warning logs for discarded jobs with
attachment/job/status context.
2. `Messages::AudioTranscriptionService`
- Keeps guaranteed temp file cleanup via `ensure`.
- Ensures temp upload files include an extension when the original
filename has none, derived from blob `content_type`.
- This addresses intermittent failures like extensionless `audio/mpeg`
files.
## Reproduction
Enable audio transcription for an account and process an audio
attachment whose stored filename has no extension (for example `speech`)
but valid audio content type (`audio/mpeg`).
Before this fix, OpenAI transcription could return HTTP 400
`Unrecognized file format` for that attachment while similar attachments
with extensions succeeded.
## Testing
Ran:
`bundle exec rubocop
enterprise/app/jobs/messages/audio_transcription_job.rb
enterprise/app/services/messages/audio_transcription_service.rb`
Result: both modified files pass lint with no offenses.
