When a reviewer saves the source language VTT during QC and confirms
the re-translate dialog, all target languages are re-translated via
Celery. Job transitions to `translating` and returns to `pending_qc`
when done. Existing polling in useJob covers progress display.
- schemas/job.py: add `retranslate_languages: bool` to VttUpdateRequest
- audit_log.py: add VTT_RETRANSLATE audit action
- translate_and_synthesize_task: accept languages/retranslate params,
filter to specified languages, skip video render, return to PENDING_QC
- routes_jobs.py: add _trigger_retranslation helper, call after VTT save
- types/api.ts: add retranslate_languages to VttUpdateRequest
- useJob.ts: invalidate all lang VTTs on retranslate
- QCDetail.tsx: confirmation dialog when saving source VTT with targets
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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