[WIP] Prepare #1012 clip processor unit tests PR

[veracindarella]

Status

This is a draft tracking PR for #1012. It contains no test or application changes; the requested processor coverage is not implemented by this PR.

Intended scope

• Add isolated unit coverage for FFmpeg success/failure and Cloudinary upload success/failure.
• Verify Prisma updates, BullMQ progress and retry/failure behavior, and error logging.
• Mock external services and assert that tests make no real external requests.
• Document existing clip-generation job/status API behavior if relevant.

Validation

Not run: this PR has no implementation changes.

Fixes #1012