Bulk Upload Media

Bulk-create entities + their media in one upload.

Designed for the AI-lab use case: a creator drops 50 generated videos that all share {model: 'Veo3', prompt: '...'} and just wants random IDs assigned. Replaces the alternative of 50 round-trips of POST /entities + POST /entities/{id}/media.

Limits:

• Up to 50 files per call (sync). Larger batches should chunk client-side.
• Total batch ≤ 1 GB (declared via Content-Length).
• All files must match the ranking's media_type. Mixed batches rejected.
• Per-file size still bounded by MEDIA_LIMITS (2 MB image, 10 MB audio, 200 MB video).

On per-file processing failure, the entity for that file is rolled back and the error is returned in the response so the client can retry just the failed ones — partial success is normal and expected for big batches.